
Class JLI^Jp, 

Book__S_:]_l^ 
Goipglit^l? 



COPyRIGHT DEPOSIE 



m 



26 ^90^ 



/5 



ROPER^S 
Practical Hand -Books 

For Engineers and Firemen. 



NEW REVISED AND ENLARGED EDITION. 

HANDY-BOOK FOR STEAM ENGINEERS 
AND ELECTRICIANS. 

PRICE, $3.50. 

pRice. 
Roper^s Catechism for Steam Engineers and Electric- 
ians, $2.00 

Roper's Questions and Answers for Steam Engineers 

and Electricians, 2.00 

Roper's Hand-Book of Land and Marine Engines, • 3.50 
Roper's Care and Management of the Steam Boiler, 2.00 
Roper's Use and Abuse of the Steam Boiler, .... 2.00 

Roper's Young Engineers' Own Book, 2,50 

Roper's Hand-Book of the Locomotive, 2.50 

Roper's Instructions and Suggestions for Engineers 

and Firemen, 2.00 

Roper's Hand-Book of Modern Steam Fire Engines, • 3.50 



DAVID MCKAY, Publisher, 

^ 1022 Market Street, Piiiladelpiiia, Pa. 



ROPER'S CATECHISM 

FOR 

STEAM ENGINEERS 

AND 

ELECTRICIANS 

INCLUDING THE CONSTEUCTION AND MANAGEMENT OF 

STEAM ENGINES, STEAM BOILERS AND 
ELECTRICAL PLANTS 

WITH ILLUSTRATIONS 
EDWIN R. KELLER, M.E. 

AND 

CLAYTON W. PIKE, B. S. 



PHILADELPHIA : 

DAVID McKAY, Publisher, 

1022 Market Street 



Offlcoofthe 

600 33 

Entered, according to Act of Congress, in the year 1873, by 

STEPHEN ROPER, 
in the Office of the Librarian of Congress, at Washington. 



Entered, according to Act of Congress, in the year 1884, by 

E. CLAXTON & COMPANY, 
in the Office of the Librarian of Congress, at Washington. 



Copyright by DAVID McKAY, 1897. 






Copyright by DAVID McKAY, 1899. 



SECOND copy. 



^3 






PREFACE TO THE TWENTY-FIRST EDITION. 



The great value of a catechism lies in the fact 
that judicious questioning emphasizes the more 
important points of a subject and also stimulates 
the mind of the student to think more definitely 
and clearly upon the subject than would be the 
case in merely reading about it. In these respects 
the written catechism is the best substitute for 
oral teaching, and the authors trust that this 
volume will be found of value for this purpose. 

The enactment of State laws requiring the 
licensing of engineers has imposed upon many 
the necessity of passing examinations for license. 
The authors likewise hope that it will prove 
useful to engineers in preparing for such exam- 
inations. . 

Edw^in R. Keller, 

Clayton W. Pike. 
Philadelphia, September, 1899. 



CONTENTS. 



For Alphabetical Index to Subjects, see page 359. 



Mechanics. p^^j. 

The Six Mechanical Elements of Machinery, . . 1 

Force, 1 

Inertia, 2 

Motion, 3 

Velocity, 4 

Acceleration, ... 4 

Falling Bodies, 5 

Mass and its Relation to Force and Acceleration, . 6 

Momentum, 7 

Energy or Work, 8 

Power, 10 

Horse-power, 10 

Parallelogram of Forces, 11 

Moment or Statical Moment, 11 

The Lever, 13 

The Wheel and Axle, 16 

The Wedge, 16 

The Pulley, 16 

The Screw, 17 

Transmission and Measueement of Powee. 

Methods of Transmitting Power, 18 

Shafting, 18 

Belting, 20 

vii 



Vlll CONTENTS. 

PAGE 

Velocity of Belts, 20 

Power Transmitted by Belts, 20 

Calculation of Width of Belt for a Given Horse- 
power, 20 

Calculation of Length of Belt Needed, 21 

Rope Driving, 22 

Gearing, 23 

Spur Gears, 24 

Friction Clutches, 25 

Pneumatic Transmission of Power, 25 

Compound Compressor, 26 

The Intercooler, 27 

Reservoirs or Receivers, 27 

Flow of Compressed Air Through Pipes, .... 28 

Efliciency of Compressed Air Systems, 28 

Electric Transmission of Power, 29 

Types of Motors, 30 

Calculation of Line, 31 

Lubricants, 32 

Best Lubricants for Different Purposes, 32 

Oil Separators, 32 

Measurement of Power, 33 

Different Methods Available, 33 

Indicator Method, 33 

Electrical Method, 34 

Prony Brake Method, 35 

HEAT, FUEL, GASES, WATER, AND STEAM. 
Heat. 

Nature of Heat, • 37 

Temperature, 37 

The Thermometer, 38 



CONTENTS. IX 

PAGE 

Thermometer Scales, 39 

Diagram for Changing from Centigrade to Fahren- 
heit Degrees, 39 

Specific Heat, 41 

Latent Heat, 41 

Unit of Heat, 41 

Mechanical Equivalent of Heat, 42 

Methods of Transferring Heat — Radiation, ... 42 

Conduction of Heat, . 42 

Conducting Power (for heat) of Various Substances, 42 

Combustion and Fuels. 

Nature of Combustion, 44 

Smoke, 44 

Fuel, Nature and Constituents of, 45 

Carbon, 45 

Air Required to Burn 1 Pound, 47 

Value of Wood as Fuel Compared to Coal, .... 47 

Heat Evolved from Various Fuels, 48 

Hydrogen in Fuel, 49 

Liquid Fuels — Petroleum, 49 

AlE. 

Oxygen, Nitrogen, and Hydrogen, 51 

Air— the Atmosphere, 52 

Atmospheric Pressure, 52 

Volume of Air at Various Temperatures, .... 53 

The Barometer, 54 

Measurement of Heights by the Barometer, ... 55 

Water. 

Composition of Water and Its Properties, .... 56 

Specific Gravity of Water, 56 



X CONTENTS. 

PAGE 

Physical States, 67 

Weight of a Cubic Foot of Water, 57 

Boiling Point, 58 

Specific Heat, 59 

Flow of Water, Head, 60 

Calculation of Pressures Corresponding to Various 

Heads, 61 

Flow from an Orifice in the Bottom of a Tank, . . 61 

Flow of Water Through Pipes, 62 

Loss of Head by Friction in Pipes, 63 

Steam. 

Steam and its Properties, 64 

Volume of Steam , 64 

Saturated Steam, . 65 

Superheated Steam, 65 

Latent Heat of Steam, 66 

Total Heat of Steam, 67 

What the Gauge Indicates, 68 

Condensation of Steam, 68 



THE STEAM BOILER. 

Plain Cylindrical Boiler, 75-77 

Cornish Boiler, 77 

Lancashire Boiler, . . . . \ 79 

Galloway Boiler, 80 

Fire-tube Boilers, 81 

Water-tube Boilers, 84 

Advantages of Water- tube Boilers, 84 

Marine Boilers, 87 

Locomotive Boilers, 89 

Horse-power Rating of Boilers, 91 



CONTENTS. XI 

PAGE 

Evaporative Power, 92 

Grate and Heating Surface, 95 

Boiler Materials, 100 

Methods of Riveting, 100 

Strength of Boilers, 102 

Boiler Setting, , . 109 

Caee and Management of Boilers. 

Water Level, Ill 

Firing, 112 

Cleaning and Blowing Off, 116 

Scale Formation and Corrosion, 123 

Foaming, 125 

Priming, 127 

ADJUNCTS OF STEAM BOILERS. 
The Safety Valve. 

Safety Valves, 128 

Spring-pop Valves, 130 

Rules and Formulae for Safety Valves, 131 

Steam Pressure Gauges, 138 

Water Columns and Gauge Cocks, 138 

Vacuum Gauges, 139 

Salinometer, 141 

The Econometer, 141 

Importance of Correct Supply of Air to the Boiler 

Furnace, 142 

Pumps and Injectors. 

Classification of Pumps, 142 

Power Required to Raise Water, 145 

Capacity of a Pump, Calculation of, 145 



L CONTENTS. 

PAGE 

Boiler Feed Pumps, 145 

Pumps for Hot Water, 146 

Injectors and Their Action, , 146 

Failure of Injectors to Work, 149 

Setting up Injectors, General Directions, .... 150 

Inspirators, 151 

Ejector or Lifter, , 151 

Comparison of Pumps with Injectors, 152 

Advantages of Heating Feed-water, 153 

Closed Type of Feed-water Heaters, 1 55 

Open Feed- water Heaters, 155 

Economizers, 159 

Furnaces and Flues, Pressure Eequired to Collapse, 1 60 

Methods of Strengthening, 162 

Grates, ... 163 

Shaking Grates, 164 

Automatic Firing, 165 

Chimneys and Stacks, 167 

Proportioning Stacks, 168 

Table of Sizes of Chimneys for Various Sizes of 

Boilers, 170 

Steam Separators, 171 

Steam Traps, 173 



THE STEAM ENGINE. 
Classification and General Description. 

Invention, 175 

Horse-power of Engines, 177 

Mean Effective Pressure, Calculation of, .... 180 

Classification of Engines, 188 

Simple and Multiple Expansion Engines, .... 191 



CONTENTS. Xlll 

PAGE 

High-speed Engines, . , 194 

Throttling and Automatic Cut-off Engines, . . . 195 

Valves and Valve Geaes. 

Various Kinds of Valves and Valve Gears, ... 197 

The Slide Valve and Its Action, 199 

The Zeuner Valve Diagram, 202 

How to Set Valves, 2U5 

Balanced Valve, 207 

Corliss Gear, 207 

Piston Valve, 207 

Separate Valves for Admission and Exhaust, . . . 207 

Steam Engine Goveenoes, 

General Principles of Operation, 209 

, Throttling Governors, 209 

Method of Action of Fly-wheel Governors, . . . 211 

Installation, Caee, and Management. 

Foundations, 213 

How to Set Up an Engine, 214 

Piping Engines, 216 

Instructions for Care of Engines, ........ 217 

Piston-rod and Valve Packing, ........ 218 

3 of Knocking and Remedies, 221 



ADJUNCTS OF THE STEAM ENGINE. 
The Steam Engine Indicatoe. 

Description of, . , o . . , . 224 

Tabor's Indicator, .... 225 

How to Attach the Indicator, . , 226 



XIV CONTENTS. 

PAGE 

Analysis of Indicator Diagrams, 228 

Mean Effective Pressure, 229 

How to Calculate the Horse-power from a Card, . 231 

CONDENSEES. 

Object of a Condenser, 233 

Surface Condenser, 233 

Jet Condensers^ 233 

The Vacuum, 234 

Power Gained by Using Condenser, 234 

MATERIALS AND THEIR PROPERTIES. 
Composition and General Peoperties. 

Elements of Matter, 236 

Atoms and Molecules, 237 

Properties of Metals, 238 

Specific Gravity, 239 

Iron — Wrought and Cast, 240 

Steel, 241 

Effect of Rise of Temperature on Tensile Strength 

of Iron, 242 

Copper, 242 

Variation of Strength with Rise of Temperature, . 242 

Alloys, 243 

Strength of Mateeials. 

Tensile and Crushing Strength, 244 

Wrought Iron ; Tensile and Crushing Strength, . 245 

Strength of Woods, 245 

Factors of Safety, 245 

Beams, 246 

Columns, 247 



ELECTRICITY. 
Fundamental Experiments, Properties, and Units. 

PAGE 

Fundamental Experiments, 248 

Ampere's Rule, 252 

Resistance, 252 

Lines of Magnetic Force, 254 

Magnetic Lines of Force Due to a Current, . . . 256 

Galvanometer, 258 

Electric Pressure Produced by Induction, .... 259 

Fleming's Rule for Direction of Induced Currents, 260 

Electro-motive Force, 266 

Units, 267 

The Ampere, Volt, Ohm, and Watt, 268 

Resistance, 270 

Conductivity, , 270 

Resistances in Multiple, 271 

Resistances in Series, 271 

Specific Resistance, 272 

Table of Relative Resistances of Conductors, . . 273 

Practical Use of Conductors and Insulators, . . . 274 

Current Effects ; Heating, 274 

Electrolytic Effects, 277 

Electro-motive Force, Methods of Producing, . . 278 

Ohm's Law and Its Application, . . 280 

Calculation of Current in Divided Circuits, . . . 282 

Electrical Measurement. 

Quantities to be Measured and Instruments 

Needed, 285 

Measurement of Current, 285 

Measurement of Electro-motive Force, 287 



XVI CONTENTS. 

PAGE 

Measurement of Resistance, 288 

Measurement of Power, 291 

Electric Batteries. 

Chemical Generators, 292 

Secondary or Storage Batteries, 292 

Primary Batteries, 293 

Open-circuit Cells, 293 

Closed-circuit Cells, 295 

DaniellCell, 295 

Bichromate Cell, 296 

Dry Cells 296 

Dynamos, 

Function of a Dynamo, 297 

Ideal Simple Dynamo, 297 

The Armature, 299 

Ring Armatures, 299 

Drum Armatures, 299 

Armature Cores, 300 

The Field, 300 

Classification of Dynamos— Series, Shunt, and 

Compound, 300 

Regulation of Shunt Dynamos, 302 

Distribution of Electrical Energy. 

Analogy to Water System, 303 

The Switchboard and Its Uses, 304 

Circuit Breakers, 304 

Ground Detector, . , . . , » . . . . 306 

Running Generators in Multiple, 307 

Systems of Distribution, 308 

Series System, 308 



CONTENTS. XVll 

PAGE 

Parallel System, 309 

Modified Systems, Three-wire, 311 

Advantages of Using High Pressures, 312 

Size of Conductors Needed, 312 

Safe Carrying Capacity of Wires, 313 

Table of Properties of Copper Wire, 315 

Methods of Carrying Conductors, 316 

Electric Lighting. 

Arc Lamps ; Classification, 320 

Requirements for Successful Operation, 320 

Constant Potential Arcs, 321 

Open Arcs, 322 

Closed Arcs, 322 

Incandescent Lamps, 323 

The Filament, 324 

Candle Powers in Commercial Use, 325 

Life and Efficiency of Lamps, 326 

Eecteic Motors. 

The Motor a Dynamo Reversed, 327 

Uses of Series, Shunt, and Compound Motors, . . 328 

Regulation of Speed, , 328 

Protective Devices, 330 

Size and Speed of Motors, 332 

Motor Generators, 333 

The Storage Battery. 

The Chloride Battery, 334 

Phenomena of Charge and Discharge, ...... 335 

Principal Sources of Trouble, 336 

Advantages in the Use of Cells, 336 

Capacity of Storage Cells, 337 



XVlll CONTENTS. 

PAGE 

Efficiency, , 337 

Method of Connecting Batteries, , . , 338 

Electeic Signals. 

Elements of all Signal Systems, . 341 

Electric Bells ; Single Stroke, 342 

Vibrating Bells, 342 

Common Arrangements of Bells, ..... . . 343 

The Annunciator, 344 

Fire Alarm Attachment, .345 

Burglar Alarm Systems, 346 

Watchmen's Time Systems, 347 

Batteries Eequired for Signal Systems, .... 349 

The Telephone. 

Properties of Sound, 350 

Telephonic Transmission of Speech ; Receiver and 

Transmitter, 35 1 

Magneto Receiver, 352 

Battery Transmitter, 353 

Improved Forms of Transmitter, 354 

The Induction Coil, 354 

The Magneto Call, 355 

Telephone Systems, Intercommunicating, .... 355 

Exchange Systems, 35(3 



ROPER'S CATECHISM 

FOR 

STEAM ENGINEERS 

AND 

ELECTRICIANS. 



MECHANICS. 

Q. Of what elements are all machines made up? 

A. Of six, known as the six mechanical ele- 
ments. These are the lever, pidley, wheel and axle, 
inclined plane, ivedge, and the screw. 

Q. For w^hat is machinery nsed ? 

A. To make force available for practical pur- 
poses. Machinery does not create force, but trans- 
mits it, diffusing it, concentrating it, or changing 
its direction. 

Q. What is force ? 

A. Force is that which produces motion or 
tends to produce it. If a force acting on a body 
meets with a resistance equal and opposite to it, 
no motion results, but pressure is exerted on the 
particles of the body. But if the force is not 
balanced, motion will take place. 
1 1 



'A roper's catechism for 

Q. What two varieties of force are there? 

A. External and internal. External forces are 
those exerted by bodies on other bodies. Internal 
forces are those exerted by the particles of a body 
on neighboring particles. The force of steam 
against the walls of the pipe or vessel containing 
it, is external. Each particle of steam exerts an 
equal amount of force on its neighbor, and this is 
an example of internal force. 

Q. What is the difference betAveen force and 
pressure ? 

A. Pressure is a particular case of force. An 
external force which, on account of a balancing 
resistance does not produce motion, is generally 
referred to as a pressure. 

Q. What is weight? 

A. The weight of a body is the force exerted by 
the earth on it (an equal amount of force is 
exerted by it on the earth). When a body rests 
on another body the upper body exerts upon the 
lower body a pressure or foixe equal to its iveight. 
The lower body exerts, of course, an equal and 
opposite force on the upper. 

Q. What is meant by inertia ? 

A. That property of matter by virtue of which 
it tends to resist a change of state. Thus, if a 
body is at rest its inertia makes it offer a resist- 
ance to any attempt to put it in motion. If a 



STEAM ENGINEERS AND ELECTRICIANS. 6 

'body is in motion its tendency is to keep moving, 
and it will do so unless some force is applied to it 
to bring it to rest. 

Q. What is motion ? , 

A. Motion is that property which matter has 
while it is changing its position. 

Q. How would you understand the term abso- 
lute motion f 

A. As a change of position, with reference to 
some fixed point in space. 

Q. What does relative motion signify ? 

A. Change of position, with reference to some 
other body which we are for the moment consider- 
ing. Thus two cars in the same train have rela- 
tive motion with regard to the station which they 
have left. They have, however, no motion rela- 
tive to each other. 

Q. What is uniform motion ? 

A. Uniform motion is that in which equal 
spaces are always passed over in equal amounts 
of time. 

Q. W^hat is variable motion? 

A. That in which equal spaces are passed over 
in unequal amounts of time. 

Q. What is accelerated motion ? 

A. That in which the space passed over in one 
second is continually increasing or diminishing. 

Q. AVhat are Newton' s laws of motion ? 



4 ROPER'S CATECHISM FOR 

A. First. A body at rest will remain at rest, or 
if in motion will continue to move uniformly in 
a straight line till it is acted upon by some force. 

Second. If a body be acted upon by several 
forces it will obey each, as if the others did not 
exist, and this will be the case whether the body 
be at rest or in motion. 

Third. If a force act to change the state of a 
body with respect to rest or motion, the body will 
offer a resistance equal to and directly opposed to 
the force. Or to every action there is opposed an 
equal and opposite reaction. 

Q. What is perpetual motion and why is it im- 
possible ? 

A. See explanation in "Roper's Engineers' 
Handy-Book," pages 6 and 7. 

Q. What is velocity ? 

A. Velocity is the rate at which motion takes 
place. If a body moves over a distance of 100 
feet in 10 seconds, its velocity is 10 feet per second. 

Q. What is uniform velocity ? 

A. Velocity is uniform when equal spaces are 
passed over in equal times. If this is not the 
case the velocity is said to be variable. 

Q. What is acceleration ? 

A. Acceleration is the rate at which the velocity 
changes, that is, the gain (or loss, as the case may 
be) in velocity in 1 second. 



STEAM ENGINEERS AND ELECTRICIANS. 5 

Q. What case of accelerated motion can you 
mention? 

A. That of a freely falling body which starts 
from rest, falls 16.1 feet the first second, 48.3 feet 
the next second, and so on. 

Q. What are the simple formulae which enable 
us to calculate the performance of falling bodies, 
when the influence of the friction of the air is 
considered of no importance ? 

A. v = l/64.4 h and h = 16.1 i\ 

Q. What is the meaning of the letters in these 
formulae ? 

A. V = velocity in feet per second; 

h = height through which the body has 

fallen, in feet; 
t = number of seconds required to fall 
through the distance h. 

Q. If a body falls from a height of 100 feet, 
what velocity will it have when it reaches the 
earth's surface? 



A. v = V 64.4 X 100 = 1/ 6440 = 80.2 feet 
per second. 

Q. How long will it take for the body to fall 
through 100 feet? 

A. h= 16.1 t' or t' = ^ ; therefore 
lb. 1 



t = \j^ = 2.49 seconds. 



100 
'16.1 



6 roper's catechism for 

Q. What is the acceleration produced by gravity? 

A. It is at the surface of the earth, about 32.2 
feet per second, and diminishes as we go up from 
the earth's surface. 

Q. What is the mass of a body ? ■ 

A. It is the quotient of the weight of the body 
divided by the value of the acceleration due to 
gravity. 

Q. Is the weight of a body everywhere the 
same? 

A. No; it diminishes as we rise from the earth's 
surface. 

Q. Is the mass always the same ? 

A. Yes; for though the weight changes, the 
value of the acceleration due to gravity changes 
to the same extent; therefore the quotient of the 
two is constant, and this by definition is the mass. 

Q. When a force is applied to a body at rest 
what is the effect ? 

A. The body is put in motion which is uni- 
formly accelerated. The acceleration produced is 
proportional to the force, as double the force act- 
ing on the same body will produce twice as much 
acceleration. 

Q. If the same force is applied to a bod}' weigh- 
ing 10 pounds and to another weighing twice as 
much, on which will it produce the greater acceler- 
ation ? 



STEAM ENGINEERS AND ELECTRICIANS. 7 

A. On the 10-pound body it will produce 
double the acceleration that it will on the 20- 
pound body. 

Q. What general rule can you give for the rela- 
tion between force, mass, and acceleration ? 

A. The force (in pounds) = the mass X accel- 
eration or with sufficient accuracy for most pur- 

,, „ the weisfht in pounds , ^, 
poses, the lorce = ^ — X the 

acceleration in feet per second. 

Q. What acceleration will a force of 20 pounds 
produce if applied to a body weighing 20 pounds ? 

A. F (force) = — v> q — ^ X A (acceleration), 

, 32.2 X F 
ox A^ 



W 
32.2 X 20 



32.2 feet per second. 



20 

This case is that of a freely falling body where 
the force due to its weight acts upon its mass tend- 
ing to accelerate it. 

Q. What is the momentum of a moving body ? 

A. It is the force which acting upon it for 1 
second will bring it to rest. It is equal to the 
product of the mass of the body by its velocity. 

Q. Has a body at rest any momentum ? 

A. No; for its velocity is zero, and hence the 
product of mass times velocity is zero also. 



O ROPER S CATECHISM FOR 

Q. What is work in the science of Mechanics? 

A. Work involves two things, force and space, 
and the amount of work is equal to the product 
of force by space. If either is absent no work is 
done. 

Q. What is the unit of work ? 

A. The foot-pound, which is the amount of work 
performed in raising a weight of 1 pound through 
a height of 1 foot. 

Q. What example can you give of forces acting 
without work being done ? 

A. A weight resting on a table exerts force, but 
as there is no motion no work is being done by 
the weight. 

Q. Was work done in placing the weight on the 
table? 

A. Yes; if the height of table is 4 feet and the 
weight is 10 pounds, the amount of work done 
was 40 foot-pounds. 

Q. What is energy ? 

A. Energy is the power of doing work. For 
example, the weight on the table has the power 
to do w^ork if it is allowed to fall from the height 
of the table. 

Q. How many forms of energy are there ? 

A. Two, — potential energy and kinetic energy. 
The energy in the weight above mentioned is a 
case of potenticd energy. A body in motion has also 



STEAM ENGINEERS AND ELECTRICIANS. 9 

the capacity for doing work stored up in it, and the 
energy resident in moving bodies is called kinetic 
energ}^ 

Q. Can you give other examples of potential 
energy ? 

A. A spring in tension or compression, a tank 
of water at a height, a reservoir of compressed 
air, a piece of coal. 

Q. Give some examples of kinetic energy. 

A. A moving train, a cannon ball, a fly-wheel, 
a stream of water, the waves of the ocean, heat, 
electric -current flow. 

Q. What is the formula for the energy in a 

moving body? 

M X V'^ 
A. E (energy in foot-pounds) = ^ , where 

M is the mass and V the velocity of the moving 

body in feet per second. In more convenient form, 

TT X F^ 
E = . ■ — , where W is the weight in pounds., 

Q. How much energy is stored up in the piston 

and piston-rod of an engine if the speed of the 

piston is 600 feet per minute, and their weight is 

100 pounds? 

. ^ 100 X 60 X 60 _„„ „ ^ , 

A. E =^ ^^^-j = 5590 foot-pounds. 

Q. What is the primary source of energy on the 
earth ? 



10 roper's catechism for 

A. The rays of the sun which raise water from 
sea-level to the clouds from which it falls in rain, 
and which causes the growth of plants from which 
has come our coal. 

Q. What is the principle of conservation of 



energy 



?* 



A. That the amount of energy in the universe 
is fixed and cannot be changed by man. He can 
transmit it and alter the form in which it appears, 
as from potential to kinetic, but can in no wise 
create or destroy it. 

Q. What is power ? 

A. Power is the rate at which work is done, or 
at which energy is changed from one form to 
another; thus, if a man lifts in one hour 100 
weights of 100 pounds each to a height of 4 feet, 
he has done work at the rate of 100 X 100 X 4, 
or 40,000 foot-pounds per hour. 

Q. What is meant by a horse-power ? 

A. Doing work at the rate of 33,000 foot- 
pounds per minute. 

Q. In the example above, what horse-power is 
the man doing? 

A. 40,000 foot-pounds per hour = —^ — foot- 
pounds per minute, or 666f foot-pounds per 

*See also "Roper's Engineers' Handy-Book," images 14 
and 15. 



STEAM ENGINEERS AND ELECTRICIANS. 11 

2 
minute ; 666f -v- 33,000 = j^ horse-power 

very nearly. 

Q. What is the rule for obtaining the horse- 
power ? 

A. To obtain the work done multiply the force 
in pounds by the distance in feet. 

To obtain the power divide this product by the 
time required to do the work, in minutes. 

To obtain the horse-power divide further by 
33,000. 

Q. How can forces be conveniently represented 
so as to calculate the effect which they will pro- 
duce on a body ? 

A. We represent each force by a line whose 
direction represents the direction of the force, and 
whose length is proportional to the amount of the 
force. 

Q. What is the principle known as the paral- 
lelogram, of forces f 

A. If two forces acting on a body be represented 
by two lines forming two adjacent sides of a 
parallelogram (their lengths being proportional to 
the strength of the forces and their directions the 
same as those of the forces), the diagonal of the 
parallelogram will represent what is called the 
resultant of the two forces, namely, a force which 
acting alone would produce on the body the same 



12 roper's catechism for 

effect as would the two forces. The direction of 
the diagonal represents the direction of the result- 
ant or equivalent force, and its length represents 
the strength of that force. 

Q. What is the resultant force which will equal 
two forces of 3 and 4 pounds, acting at the same , 
point and at an angle of 90 degrees ? 

A. Lay out the line A B with 4 units of length 
to represent the force of 4 pounds, and A C with 
3 units of length at right angles to A B, to repre- 
sent the other force. 
Complete the parallelo- 
gram by drawing B D 
and C D; then the diag- 
onal A D will represent 
the resultant, and if 
measured or calculated 
its length will be found to be 5 units. The result- 
ant force will then be 5 pounds exerted at an 
angle of 36° 53^ to the hne A B. 

Q. What will be the resultant of a force of 10 
pounds in one direction and a force of 5 pounds 
acting in the same line but in the opposite direc- 
tion ? 

A. 10 less 5, or 5 pounds. When the forces are 
parallel or in the same line no parallelogram can 
be formed. 

Q. What is the moment of a force ? 




STEAM ENGINEERS AND ELECTRICIANS. 13 

A. It is the number which represents its ten- 
dency to cause rotation about a certain point. For 
example, if a stick 5 feet long is pivoted at one 
end and if a force of 5 pounds be applied at the 
other end, the force would tend to make the stick 
rotate about the pivot point. This tendency 
would be greater if the force were greater or if the 
length of the stick were greater. It is, in fact, 
proportional to the product of the force by the 
perpendicular distance from the pivot point to 
the line of direction of the force, and this product 
is technically known as the moment of the force 
about the pivot point. 

Q. What is the particular value of the idea of 
moments ? 

A. It gives a simple treatment of levers and 
questions governing the rotation of bodies. 

Q. AVhat is the general principle of moments 
as applied to levers ? 

A. When two forces are acting at different 
points in the same body, if the moments, taken 
about a given point, of the forces are equal and 
opposed in direction, the body will be at rest, 
otherwise the body will be set in motion. When 
there are more than two forces they may be 
divided into two sets, — one set tending to rotate 
the body in one direction about the point, and the 
other set tending to rotate the body in the other 



14 roper's catechism for 

direction. If the sum of the moments of the 
first set of forces is equal to the sum of the 
moments of the second set, the body will be at 
rest; but if the sums of the moments of the two 
sets of forces are unequal, the body will be set in 
motion. 

Q. How does this principle apply to levers ? 

A. In the use of levers, as, for example, the case 
of a man trjdng to raise a rock by means of a 
crowbar, we have three forces applied at three 
different points of the crowbar, — one force the 
strength of the man, another the weight of the 
rock, and the third the upward thrust of the point 
of support. By taking moments about the point 
of support, the moment of the third force becomes 
zero, since its lever arm is zero, and the bar is in 
equilibrium under the action of two equal moments. 
If one force is known, as, for example, the weight 
of the rock, we can calculate the force which must 
be applied by the man. If the moment of the 
force used by the man is the greater, he will move 
the rock; if less, he cannot do so. 

Q. What three classes of levers are there ? 

A. First Those in which the fulcrum or point 
of support is between the applied force and the 
resisting force. 

Second. Those in which the resisting force is 
between the applied force and the fulcrum. 



STEAM ENGINEERS AND ELECTRICIANS. 15 

Third. Those in which the apphed force is 
between the fulcrum and the resisting force. 

Q. With a lever of the first class, 10 feet long, 
what force must be applied at the end to lift a 
weight of 9000 pounds, if the fulcrum is distant 
from the weight 1 foot? 

A. Call the force F. Then by the principle of 
moments, when the applied force is just sufficient 
to balance the weight, i^ X 9 = 9000 X 1, or i^ = 
9000 -- 9 = 1000 pounds. 

Q. Is any 'power gained by using a lever, or, 
more accurately speaking, is any energy gained ? 

A. No; the same expenditure of work is re- 
quired to raise a weight of 9000 pounds, whatever 
may be the machinery used to perform the work. 
A lever merely allows a person, too weak to lift a 
certain weight with the hands, to do so by taking 
a longer time to perform the act. Looked at from 
the standpoint of work, if the 9000 pounds is 
lifted 1 foot in height, 9000 foot-pounds of work 
are done. The end of the lever at which the 
force of 1000 pounds is applied, moves through a 
distance of 9 feet if the other end moves through 
1 foot. Therefore, the work done, which is always 
the product of force times distance through which 
the force is exerted, is 1000 X 9, or 9000 foot- 
pounds, the same as if the stone were lifted 
directly. 



16 



ROPER S CATECHISM FOR 



In one sense it may be said that we gain force 
by the use of the lever, in that we can, by taking 
a longer time to do the work, get along with a 
smaller force. 

Q. How does the wheel and axle differ from a 
lever ? 

A. The wheel and axle may be considered as a 
lever in which the points of support and resist-" 
ance are continually renewed. The center of the 
axis is the fulcrum, the radius of the wheel is the 
long arm and the radius of the axle the short 
arm of the lever. 

Q. What is the relation between the applied 
force and the resulting force in the case of a wedge ? 
A. If a force of F pounds be applied at the 
point B in the direc- 
tion B A, the resulting 
force W (in a direction 
perpendicular to A B) 
will have the follow- 
ing relation : 

W_ _ len gth A B 
F ~~ length C D* 
Q. What two kinds of pulleys are there ? 
A. The fixed, which only turns on its axis, and 
the movable, which moves up and down as well as 
turns on its axis. 

Q. What is the use of a fixed pulley? 




STEAM ENGINEERS AND ELECTRICIANS. 17 

A. Merely to change the direction of force. 

Q. What advantage is gained by a movable 
pulley ? 

A. It enables us to raise a weight by the appli- 
cation of a force half as great as the weight, 
although we take twice as long to do the work. 

Q. With two movable pulleys what would be 
the gain ? 

A. We should need a force of only one-quarter 
the weight. 

Q. Does it make any difference whether the 
movable pulleys are separate or consist of sheaves 
mounted in the same case ? 

A. No. 

Q. Give the general rule for finding the force 
necessary to lift a certain weight with the ordinary 
block and tackle. 

A, Divide the weight by the number of sheaves 
hi the movable pulley. 

Q. What is the rule for finding the force which 
must be applied at the end of the lever of a jack- 
scrcAv in order to lift a certain weight ? 

A. Multiply the weight by the pitch of the 
screw, in inches, and divide by 6.2832 times the 
length of the lever, also expressed in inches.* 

*For complete explanation, see "Eoper's Engineers' 
Handy-Book," pages 23 and 24. 



18 roper's catechism for 

POWER TRANSMISSION AND 
MEASUREMENT* 

SHAFTING. 

Q. What are the principal methods of trans- 
mitting power ? 

A. By shafting with pulleys and belts. 
By rope driving. 
By gear wheels. 
Hydraulic. 

Pneumatic, by compressed air. 
Electrical, b}^ dynamos, line, and motors. 
Q. Why is shafting now made of steel instead 
of iron? 

A. Because a steel shaft for the same weight 
and size is stronger with respect to the twisting 
strain, and stiffer as regards transverse strains due 
to the weight of pulleys and pull of belts. 

Q. What two requirements must be met by 
shafting ? 

A. It must be large enough to transmit the 
required power at the given speed without being 
twisted too much. It must also have sufficient 
size to stand the transverse pull due to its own 
weight, the weight of the pulleys, and the weight 
and pull of the belts. 

Q. What general rule should guide the location 
of hangers? 



STEAM ENGINEERS AND ELECTRICIANS. 19 

A. They should be as near as possible to the 
pulleys, and should not be over 8 feet apart for 
light shafting. 

Q. Give the rule for calculating the diameter of 
a shaft to transmit a certain horse-power at a cer- 
tain number of revolutions per minute. 

A. Multiply the horse-power by 70 and divide 
by the number of revolutions per minute, and 
extract the cube root of the quotient. The result 
will be the diameter of the shaft in inches. 

Q. What is the rule for obtaining the greatest 
allowable distance between hangers for a certain 
size of shaft? 

A. Multiply the square of the diameter in 
inches by 140 and extract the cube root. The 
result will be the distance in feet. 

Q. What is the rule for finding the number of 
horse-power which a shaft of a certain diameter 
will transmit at a certain speed? 

A. Multiply the cube of the diameter in inches 
by the number of revolutions per minute and 
divide the product by 70. 

Q. Can these rules be depended upon for all 
cases ? 

A, No; only for ordinarily heavy pulleys. For 
any very heavy pulleys the diameters given by 
these rules would be too small. 



20 roper's catechism for 



BELTING. 

Q. What are the advantages of leather over 
rubber belts ? 

A. Leather belts have a longer life, and are less 
affected by oil and by heat and cold. They will 
stand being run through shifters or crossed. 
When worn they can be cut up into narrower 
belts, whereas rubber belts when worn are of no 
use. 

Q. What two points determine the width of a 
belt for transmitting a certain horse-power ? 

A. The speed at which the belt runs and the safe 
working-strain of the belt, which may be taken 
as 45 pounds per inch width for single belting. 

Q. How much more power will a belt transmit 
when running at 6000 feet per minute than at a 
speed of 3000 feet per minute ? 

A. Twice as much. 

Q. At about what speed is it best to run belts ? 

A. Between 4000 and 5000 feet per minute. 

Q. What is a common rule for determining the 
width of belt to transmit a certain horse-power ? 

A. That a belt 1 inch wide, at a speed of 1000 
feet per minute, will transmit 1 horse-power; a 2- 
inch belt will transmit 2 horse-power, and so on. 

Q. Is this rule a safe one to follow ? 

A. Yes; for the most favorable cases, where the 



STEAM ENGINEERS AND ELECTRICIANS. 21 

belts are open and horizontal, with a long distance 
between centers, a narrower belt may be used. 

Q. Will a belt 30 feet long transmit more power 
than the same belt 20 feet long ? 

A. Yes, if it is horizontal; for owing to the 
greater weight of the longer belt it will sag down 
a little more in the center and give a little greater 
arc of contact on the pulleys. 

Q. What is the objection to vertical belts? 

A. The weight of the belt tends to pull it away 
from contact with the lower pulley and, therefore, 
to transmit a given power a vertical belt must be 
run tighter than if it were horizontal. Moreover, 
with a horizontal belt the upper side tends to sag 
down owing to its weight, and this increases the 
arc of contact with the pulley. 

Q. Why do the formulae of different authors 
for finding the width of belts differ so much ? 

A. Because some use a greater permissible ten- 
sion on the belt than others, which shortens the 
life of the belt and renders repairs more frequent.* 

Q. What is the rule for obtaining the length of 
an open belt? 

A. Multiply the sum of the diameters of the 
two pulleys by 3.1416 and divide by 2. To the 
quotient add twice the distance between centers. 

*See Belting, "Roper's Engineers' Handy-Book," pages 
34-43. 



22 roper's catechism for 

Q. Is this rule strictly accurate ? 

A. Yes, if the diameters of the pulleys are the 
same; if not, the result is slightly too small. 

Q. How would you measure the length of a belt 
in a coil ? 

A. Add the outside diameter to the diameter of 
the hole and divide by 2. This would give the 
mean diameter which should be expressed in feet. 
Then multiply this by 3.1416 and the product by 
the number of coils in the roll. 

Q. How would you determine the proper size of 
a driven pulley to run at a certain number of 
revolutions per minute, having given the diameter 
and speed of the driving pulley ? 

A. Multiply the diameter of the driver by the 
number of revolutions which it makes per minute 
and divide the product by the number of revolu- 
tions which the driven pulley is to make. 

Q. In arranging for belting, which side should 
be the loose side, the upper or lower ? 

A. The upper, so that the weight of the belt 
may make it sag down and thus make a longer arc 
of contact between belt and pulleys. 

Q. What advantages does rope transmission 
have over belt driving ? 

A. The cost of rope is less than that of belting, 
and the pulleys do not have to be so accurately 
lined up. 



STEAM ENGINEERS AND ELECTRICIANS. 23 

Q. What are the two general methods of using 
ropes ? 

A. First. To put ropes on hke so many parallel 
spliced belts, one working in each groove of the 
pulley. 

Secondly. To wrap the rope around the pulleys 
as many times as there are grooves, then to carry 
it through idlers so arranged that the tension can 
be varied, and then to carry the rope back to the 
starting-point and to splice it. 

Q. What is the objection to the first method? 

A. The separate ropes do not all pull equally. 

Q. How is this partially overcome ? 

A. By making the grooves of the smaller pulley 
with a sharper angle. 

Q. At what speeds do the ropes run ? 

A. At speeds varying from 25 to 100 feet per sec- 
ond, the most common practice being about 80 feet. 

Q. Can you give any figures showing what 
horse-power is transmitted by a certain size rope ? 

A. A 1-inch rope 'at a velocity of 5000 feet per 
minute will transmit about 13 horse-power. 

TOOTHED AND FRICTION GEARING. 

Q. What is the pitch of a gear wheel ? 

A. The distance measured along the pitch circle 
from a point on one tooth to the corresponding 
point on the next tooth. 



24 eoper's catechjsm for 

Q. What is the thickness of a gear tooth ? 

A. Its width measured along the pitch circle. 

Q. What is the space f 

A. The difference between its pitch and its thick- 
ness. 

Q. What is backlash f 

A. The amount by which the space is greater 
than the thickness. 

Q. What are spur gears used for ? 

A. To connect parallel shafts. 

Q. When are bevel gears used ? 

A. When it is desired to connect shafts making 
an angle with each other. 

Q. What are the two principal forms of gear 
teeth ? 

A. The cycloid and the involute, the latter being 
used when the number of teeth is small. 

Q. How would you calculate the diameter or 
number of teeth in a driven wheel to run a certain 
speed having given the diameter or number of 
teeth of the driver? 

A. Just as the diameter of a driven pulley is 
calculated. * 

Q. For what are friction-clutch connections 
principally used ? 

A. To take the place of tight and loose pulleys, 

*See also "Roper's Engineers' Handy-Book," pages 
50-52. 



STEAM ENGINEERS AND ELECTRICIANS. 25 

and to connect two or more sections of a line of 
shafting so that the sections may be disconnected 
or thrown together without, stopping the shaft. 

Q. Describe the general principle on which most 
friction clutches are constructed. 

A. A pulley is mounted so as to turn freely on 
a sleeve in which the shaft turns. This pulley 
has either a special rim attached to the arms or 
else a disk attached to the hub, which is gripped 
between the jaws of the clutch device. The 
clutch is mounted on and keyed to the shaft. The 
jaws of the clutch are made to open or shut by 
moving the clutch collar in one direction or another 
along the shaft by a fork handle. The motion of 
the clutch collar operates some kind of toggle joint 
which moves the jaws; when the jaws are closed 
so as to grip the rim or disk, the pulley is made 
to turn with the shaft. 

COMPRESSED AIR. 

Q. What are some of the purposes for which 
compressed air is used as a means of transmitting 
power ? 

A. For operating cranes, hoists, drills, rivet- 
ing-machines, coal-mining machinery, railroad 
signals, shop tools, sand blasts, brakes, etc. 

Q. Describe the general method of power trans- 
mission by compressed air. 



26 roper's catechism for 

A. Air is compressed by some form of piston 
pump driven by a steam engine, water wheel, 
electric motor, or anj;^ convenient source of power. 
Pipes carry the compressed air to the point where 
it is to be used, where it is led into the air motor 
or other machine in which it is to be used. 

Q. What is the general nature of the air motor ? 

A. An ordinary steam engine or steam pump 
may be used as a compressed air motor, according 
as rotary or reciprocating motion is desired. Com- 
mercial motors differ from these only in form and 
detail. 

Q. Why in steam-driven air compressors is the 
duplex or compound type used so largely ? 

A. With a single steam and single air cylinder 
the maximum steam pressure is at the beginning 
of the stroke, while in the air cylinder the great- 
est pressure is at the end of the stroke. This is 
equalized to a great extent by having two cylinders 
of different sizes and performing the first part of 
the compression in the larger and finishing it in 
the smaller cylinder. 

Q. Has the compound compressor any other 
advantage ? 

A. Yes; it is more efficient, i. e., it com^Dresses 
a greater quantity of air with a given amount of 
steam than would a simple compressor. 

Q. What is the intercooler ? 



STEAM ENGINEERS AND ELECTRICIANS. 27 

A. A tank containing coils through which runs 
cold water. This tank is so connected between 
the large and small air cylinders that after the 
air has received the first part of its compression it 
is led through the intercooler before it passes into 
the second compressing cylinder. 

Q. What is the advantage of the intercooler ? 

A. The air being cooled after the first com- 
pression it does not reach so high a temperature 
in the second cylinder, so that lubrication is much 
easier ; moreover, it is found that by using the 
intercooler a given quantity of air can be com- 
pressed with the use of a less quantity of steam 
than would be the case without it. 

Q. How much of a saving in steam is attained 
by the cooling of the air? 

A. About 10 per cent, by the intercooler and 5 
per cent, by the water jackets around the air-com- 
pressing cylinders. 

Q. How is the regulation of air pressure main- 
tained ? 

A. By a balanced valve operating a little piston 
which in turn operates another controlling the 
steam supply for the steam cylinder of the com- 
pressor. 

Q. What are receivers and why are they used ? 

A. They are steel tanks of suitable size and 
strength, placed one near the compressor and one 



28 roper's catechism for 

near the point where the air is to be used. Their 
object is to prevent fluctuations of pressure in the 
system. They thus preserve a steady flow of air 
in the pipe hne and keep the loss of pressure by 
friction down to a minimum. 

Q. AVhat is a common pressure for compressed- 
air systems ? 

A. 80 pounds. 

Q. How does the loss of pressure due to fric- 
tion of air flowing through pipes vary ? 

A. In proportion to the length of pipe and in 
proportion to the square of the velocity or quan- 
tity per minute which goes through the pipe. 

Q. Can you give any figures showing the num- 
ber of cubic feet of compressed air used by air 
motors ? 

A. In small motors of, say, one horse-power 
about 700 cubic feet per horse-power per hour; 
with large motors as low as 500 cubic feet per 
horse-power per hour. 

Q. What percentage of the power put into the 
air compressor would j^ou expect to get out of the 
air motors? In other words, what would be the 
efficiency of a complete pneumatic transmission 
system ? 

A. From 35 to 55 per cent. 



STEAM ENGINEERS AND ELECTRICIANS. 29 



ELECTRIC TRANSMISSION OF POWER. 

Q. Describe the general method of transmitting 
power electrically. 

A. The energy of a steam engine, water wheel, 
or other source of power is used to drive an elec- 
trical generator or dynamo, which changes energy 
from the mechanical form into the electrical form. 
This electrical energy is conveyed from the gener- 
ator by insulated copper wires of suitable size to 
the point where it is desired to use the energy. 
At that point electric motors or other electric 
devices are attached to the wires and change the 
energy back again intf the mechanical form. 

Q. What two classel of transmission are there? 

A. Transmission by direct current and trans- 
mission by alternating current. 

Q. In the electrical transmission of power when 
would you, generally speaking, use an alternating 
current transmission, and why ? 

A. When the distance is over 1500 feet, — be- 
cause it requires a smaller conductor to transmit 
a certain power if the pressure used be high than 
if it be low, and alternating currents can more 
readily be changed from high to low pressure than 
can direct currents, and are therefore more con- 
venient to use when high pressures are employed.* 

*See also "Roper's Engineers' Handy-Book," page 65. 



30 roper's catechism for 

Q. What three types of direct-current motors 
are there ? 

A. The shunt wound, the series wound, and 
the compound wound.* 

Q. For what class of service are these types 
used? 

A. The series motor is used on hoists and 
street-car motors, where constancy of speed is not 
necessary, but where a strong starting-torque is 
desired. The shunt motor is used for the greater 
part of the work requiring constant speed, the 
compound motor being used in a few special 
cases. 

Q. What type of direct-current motor is gener- 
ally used for driving machine tools ? 

A. The shunt-wound motor, because it naturally 
runs at nearly constant speed at all loads. 

Q. Suppose, as with a lathe, we wish to get 
several different speeds, how is this accomplished ? 

A. By a regulating rheostat or controller. 

Q. What is the gain, in size of wire used on 
the line, if we employ a 220-volt system instead 
of a 110-volt system? 

A. The 220-volt system requires but one-quarter 
the weight of copper in the line. 

Q. Do any disadvantages occur to you ? 

A. The 220-volt line and motor are a little 
* For a description of these types see page 300. 



STEAM ENGINEERS AND ELECTRICIANS. 31 

more difficult to insulate from the earth, and they 
are therefore slightly more liable to cause trouble 
from leakage-currents and accidental shocks. 

Q, Is the shock from 220 volts dangerous ? 

A. Not unless taken by a person in exceedingly 
delicate health. 

Q, Is the shock from 550 volts dangerous ? 

A. It is exceedingly severe, although rarely, if 
ever, fatal. 

Q. What determines the size of wire to be used 
for connecting a generator and motor ? 

A. The power to be transmitted, the pressure 
used, the distance, and the permissible loss in 
pressure. 

Q. What determines the allowable loss? 

A. The variation in speed of the motor, between 
no load and full load, which you are willing to 
allow. 

Q. Even with no loss of pressure in the line, 
what variation of speed would you expect with 
the average small motor ? 

A. About 3 per cent. 

Q. How would you calculate the size of wire, 
having given the power, pressure, distance, and 
permissible loss ? . 

A. See "Roper's Engineers' Handy-Book," 
pages 67, 717, 718. 



32 eoper's catechism for 

LUBRICATION. 

Q. What is the object of a lubricant? 

A. To diminish friction by interposing a thin 
film between the revolving or sliding surfaces. 

Q. Does any lubricant have any tendency to 
improve a bearing ? 

A. No; it simply keeps the surfaces apart, 
diminishes friction and prevents overheating. 

Q. What are the requirements for a good lubri- 
cant ? 

A. It must have sufficient body to keep the 
surfaces apart, but must be as fluid as possible 
consistent with this requirement. It must have 
the smallest possible friction, must not gum or 
corrode; it must have a high flashing-point, and 
must remain fluid at the lowest temperature at 
which it will be used. 

Q. W^hat would you use for slow speeds and 
heavy pressures on the bearings ? 

A. Graphite, soapstone, tallow, or grease. 

Q. What is an oib separator and on w^hat prin- 
ciple does it operate ? 

A. A device for separating the oil from the 
steam coming from the exhaust of an engine. 
The principle on which it operates is to destroy 
the momentum of the oil which is carried along 
with the steam. This is accomplished by baffle 



STEAM ENGINEERS AND ELECTRICIANS. 33 

plates which alter or reverse the direction of flow 
of the steam. The heavy oil particles are thus 
thrown against the plates and are given time to 
fall under the action of gravity into a chamber 
from which they may be afterward drawn off. 

MEASUREMENT OF POWER. 

Q. What are three common methods of measur- 
ing power ? 

A. By means of the steam-engine indicator, by 
electrical methods, and by the Prony brake or 
some other form of dynamometer. 

Q. Which is the most accurate ? 

A. Whenever the electrical method can be ap- 
plied it is the quickest and most accurate. 

Q. How would you determine by the indicator 
method the power used by a certain tool ? 

A. By indicating the engine with the tool run- 
ning and without it. The difference in the power 
shown by the two cards gives the power used by 
the tool. 

Q. Is this method accurate ? 

A. Not if the power used by the tool is small 
compared to the power of the engine. In this 
case it is like trying to weigh a fly on a platform 
scale, by weighing a man on the scale with the fly, 
and then weighing the man without the fly and 
subtracting one weight from the other. 
3 



34 eoper's catechism for 

Q. What instruments would you require for the 
electrical method, if direct currents were used ? 

A. An amperemeter and voltmeter of proper 
range or a wattmeter, though the latter is much 
less commonly at hand. 

Q. How Avould you measure the power used in 
operating a tool driven by a direct-current electric 
motor ? 

A. I would measure the electrical pressure 
betw^een the two terminals of the motor by con- 
necting to the terminals a voltmeter of suitable 
range; I would at the same time find what current 
was supplied to the motor by connecting an am- 
meter in the circuit suppling the motor; I would 
take several readings of both instruments and 
would multiply the average reading of the volt- 
meter in volts by the average reading of the am- 
meter in amperes; this product I would divide 
by 746, and the quotient would be the electrical 
horse-power supplied to the motor; then I would 
throw off the belt betw^een the motor and tool and 
repeat the measurement above so as to get the 
horse-power used by the motor when running 
idle; subtracting this from the total power sup- 
plied to the motor would give the power used by 
the tool. 

Q. "Will this method be correct if the motor is 
of the alternating current type ? 



STEAM ENGINEERS AND ELECTRICIANS. 35 

A. No; for the product of volts and amperes 
does not give the power. In this case a watt- 
meter must be used. 

Q. Describe the Prony brake. 

A. The Prony brake consists of two or more 
blocks of wood at- ^ » 

tached to a lever arm, j* — ^™V 

and so arranged that 3(^^31== © — = 

they can be clamped v — 9 

more or less tightly to 

a pulley or shaft, the 

power transmitted by which it is desired to measure. 

Q. How is the powder measured ? 

A. When the blocks are clamped to the pulley 

or shaft the tendency is for the Prony brake to 

revolve with the shaft, but weights are put in the 

pan hanging from the end of the brake-arm, 

until this tendency is balanced and the arm stands 

horizontal. The number of revolutions, R, the 

weight, W, and the length, L, from the center of 

the shaft to the point of the lever to which the 

weight pan hangs, are noted. The horse-power is 

calculated from the formula — 

^ WXLXRXQ-28 
Horse-power = ^^^ , 

or if the distance L is made 5' 3'', the formula 
WX R 



becomes, Horse-power = 



1000 



36 roper's catechism for 

Q. AVhat may be substituted for the pan and 
weights ? 

A. A spring balance, the average of its read- 
ings being used. 

Q. What is a dynamometer ? 

A. Any instrument used to measure power, as, 
for example, the Prony brake. 

Q. For what purpose is a spring dynamometer 
used ? 

A. For measuring the power required to propel 
vehicles, such as carriages, street-cars, or railway 
coaches. 



STEAM ENGINEERS AND ELECTRICIANS. 37 

HEAT, FUEL, AIR, W ATER, AND STEAM. 

HEAT. 

Q. What is heat? 

A. Heat is a form of energy. In any body its 
molecules are in a state of incessant oscillating 
motion, and the energy of these moving molecules 
or particles of the body is the heat of that body.* 

Q. What is temperature, and how does it differ 
from heat ? 

A. Temperature is a measure, not of the heat 
in a body, but of the tendency of that body to 
give up its heat to other bodies. Two bodies 
may be at the same temperature and yet possess 
very different quantities of heat. For example, 
a cubic inch of iron and a cubic foot of iron may 
both be put in the same oven, and after remaining 
there for a considerable time they would be at the 
same temperature as would be shown by a ther- 
mometer. But the cubic foot of iron has 1728 
times as many heat-units in it as the cubic inch, as 
could be proved by putting them in equal quanti- 
ties of water, and noting to what temperature the 
water is raised in each case. According to the 
molecular theory of the structure of matter a 
higher temperature means that the molecules of 

* For the explanation of the molecular theory of matter, 
see " Roper's Engineers' Handy-Book," page 611. 



38 roper's catechism for 

the body are moving more rapidly. They, there- 
fore, will communicate motion to surrounding 
bodies the more readil}^, and this is the reason 
that bodies at high temperatures give up heat to 
those at the lower temperatures. A lower tem- 
perature means that the velocity of the molecules 
is less, and as the temjoerature gets lower and 
lower their velocity would become smaller and 
smaller until a temperature is reached at which 
their velocity is zero, that is, they are at rest. 
This temperature is known as the absolute zero of 
temperatures. 

Q. How is temperature measured ? 

A. By means of a thermometer. 

Q. How is a thermometer usually made ? 

A. A thermometer consists usually of a small 
hollow glass tube with a bulb at its lower end. 
The air having been exhausted from the tube it is 
partially filled with mercury and sealed. The 
tube is placed in melting ice and the position of 
the top of the mercury column marked on the 
glass. The same thing is done with the tube 
placed in boiling water. The distance between 
these two marks is divided into a certain number 
of equal parts, according to which scale is used. 

Q. What are the three thermometer scales in 
common use ? 

A. The Fahrenheit, Centigrade, and Reaumur. 



STEAM ENGINEERS AND ELECTRICIANS. 



39 



COMPARISON OF FAHRENHEIT, CENTIGRADE, AND 
REAUMUR SCALES. 



CENT. 

"Drill {•r./Y- t^,^i'ti+ 4 AA _^.^ 


FAHR. 
?1? 


REAU. 


xsoiiing-point XvO ^^^ 




"~~~ qQ Jt>oiiing-point 


of water. 


200 


of water. 


90 — 


190 

180 


— 70 


80 — 


170- 


— 60 


70 — 


160 

150 

140 




60 — 


— 50 




150 




so- 


180 


— 40 


lo — 


110 






-100 


— zo 


50 — 


90 

80 






— 20 


20 — 


70 

60 




f A 




— 10 


lu — 


40 




Freezing-point. ■ 


OX, 


^— — Q Freezing-point. 


-10 — 


to 

10 



10 


—10 


-20 — 






20 


-30— 


20 








TVTpjTPnTTT fTPPr^fia — M£^ 




° 


ATiOJL^Ul J' iiCC/iC&« '^••li ^^^^^ 





40 roper's catechism for 

Q. Where is the Fahrenheit scale used ? 

A. The Fahrenheit scale is used in England, 
Canada, and in the United States. 

Q. What is the difference between Fahrenheit's, 
Centigrade, and Reaumur' s scales ? 

A. Fahrenheit's zero is 32° below freezing, Ijoil- 
ing-point of water, 212°; Centigrade zero is at 
freezing, boiling-point, 100°; Reaumur's zero is at 
freezing, boiling-point, 80°. Hence, 180 Fahren- 
heit degrees are equal to 100 Centigrade degrees 
or 80 Reaumur degrees, or 9 Fahrenheit degrees 
are equal to 5 Centigrade or 4 Reaumur degrees. 

Q. What are fixed temperatures ? 

A. One the melting-point of ice, and the other 
the boiling-point of pure water. 

Q. Why do you call these fixed temperatures ? 

A. Because it is impossible to raise the tempera- 
ture of ice above 32° Fahr., and no amount of 
heat will raise boiling water above a temperature 
of 212° Fahr., if contained in an open vessel. 

Q. Does the thermometer indicate the amount 
of heat in any body ? 

A. No; only the changes in temperature. 

Q. To how high temperatures can the mercurial 
thermometer be used ? 

A. To about 600° Fahr. At about 675° mer- 
cury vaporizes. 

Q. What method is adopted to determine tern- 



STEAM ENGINEERS AND ELECTRICIANS. 41 

peratures so high that no thermometer can give a 
rehable result, as, for example, the temperature 
in a blast furnace ? 

A. We take a body, such as platinum, and 
place a mass of this metal in the blast furnace, 
and when the mass has acquired the temperature of 
the furnace we transfer it to a vessel containing a 
,, known weight of water. We can then observe 
the rise of temperature by means of an ordinary 
thermometer, and from this and the weight of the 
platinum and its specific heat (.0324) we can 
calculate the temperature. 

Q. What is specific heat ? 

A. Specific heat of a substance is an expression 
for the quantity of heat in any given weight of it 
at certain temperatures. It is the number of 
heat-units necessary to raise the temperature of 
1 pound of the substance 1 degree. 

Q. What is sensible heat ? 

A. That which is sensible to the touch. 

Q. What is latent heat ? 

A. It is that which a body absorbs in changing 
from a solid to a fluid state, called the latent heat 
of liquefaction, or that which it absorbs in chang- 
ing from the liquid to the gaseous state, called the 
latent heat of vaporization. 

Q. What is a unit of heat ? 

A. The unit of heat is the amount of heat 



42 roper's catechism for 

required to raise the temperature of 1 pound of 
water 1°, or from 32° to 33° Fahr. 
' Q. What is the mechanical equivalent of heat ? 

A. The energy necessary to raise 1 pound 778 
feet high ; that is, 778 foot-pounds of mechanical 
energy, if used to produce heat, will be just equal 
to 1 heat-unit, being just able to raise the tem- 
perature of 1 pound of water 1° Fahr. 

Q. How is heat transferred from one body to 
another ? 

A. In three ways, — by radiation, by conductioHj] 
and by convection.* 

Q. What substances radiate heat most readily 1 

A. Those which absorb it most readily and 
reflect it the least. 

Q. What color should the covering of steam 
pipes be painted ? 

A. White, because white radiates less than 
dark colors. 

Q. If the pipe is bare, as, for instance, a copper 
pipe, should it be kept burnished or dull ? 

A. Burnished. 

Q. What are some of the best conductors of 
heat? 

A. Generally speaking, the metals, of which 
silver, copper, and gold are the best. 

*For full explanation, see " Eoper's Engineers' Handy- 
Book, ' ' page 94. 



STEAM ENGINEERS AND ELECTRICIANS. 43 

Q. Is there any similarity between heat conduc- 
tivity and electrical conductivity ? 

A. Generally speaking, good conductors for 
heat are also good conductors electrically, although 
the metals do not stand in the same relative order 
for both cases. 

Q. What are some of the best non-conductors ? 

A. Magnesia, mineral wool, hair felt, cork, air 
(not in motion). 

Q. To what practical use are non-conductors of 
heat put ? 

A. To the covering of steam pipes. 

Q. Apart from the waste of fuel clue to loss of 
heat by radiation from steam pipes, is there any 
other effect ? 

A. Yes; there is a lowering of pressure and a 
condensation of steam into water, which, if exces- 
sive, would cause trouble in an engine. 

Q. How much heat does a pound of water 
receive in passing from a liquid at 212° Fahr. to 
avapor at 212°? 

A. It receives as much heat as would raise it 
966° if the heat was sensible instead of latent. 

Q. What is convection of heat ? 

A. It is the transfer or diffusion of heat in a 
fluid mass by means of its particles. 

Q. Will water boil in a vacuum with less heat 
than under the pressure of the atmosphere ? 



44 roper's catechism for 

A. Yes; in a vacuum of 1 pound absolute pres- 
sure water boils at 98° to 100°. 

Q. Does water give out heat in freezing ? 

A. Yes; water in freezing gives 142 heat- 
units. 

Q. AVhat is a thermal unit? 

A. It is the quantity of heat required to raise 1 
pound of water 1°, the water being at its maxi- 
mum density (=39° Fahr. ). It is also called a 
British thermal unit, and is abbreviated B. T. U. 

COMBUSTION AND FUELS. ' ■ 

Q. What is combustion ? 

A. Combustion is a chemical process which 
takes place rapidly, in which the one or more of 
the elements which make up the combustible body 
combines with the oxygen of the air. Briefly, 
combustion is a rapid oxidation accompanied by 
flame or fire. 

Q. What is smoke ? 

A. Smoke is the result of imperfect combustion, 
and its appearance is due to minute unburned 
particles in the air. 

Q. What is necessar}^ to produce complete com- 
bustion ? 

A. We must have sufficient air, must mix the 
combustible thoroughly with the air, and must 
maintain the combustible and air mixed with it 



STEAM ENGINEERS AND ELECTRICIANS. 45 

at a temperature above the igniting-point of the 
combustible. 

Q. What is the meaning of the term fuel ? 

A. Fuel is used to denote substances that may 
be burned with air rapidly enough to produce 
sufficient heat for commercial purposes. 

Q. What sort of substances does fuel consist of ? 

A. Of vegetable substances or the products of 
their decomposition. 

Q. What are some of the principal fuels used 
in the production of steam ? 

A. Coal, coke, wood, petroleum, natural gas, 
peat, and vegetable refuse of various kinds. 

Q. What are the elementary substances which 
are found in most fuels ? 

A. Carbon, hydrogen, oxygen, nitrogen, and 
small quantities of other elements. 

Q. What is the chief constituent of coal ? 

A. Carbon. 

Q. How much carbon does good coal contain ? 

A. Anthracite contains about 90 per cent. 

Q. Are there any other elements in coal except 
carbon ? 

A. Yes ; hydrogen, nitrogen, and sulphur in 
small quantities. 

Q. How much heat does 1 pound of pure car- 
bon yield in burning ? 

A. 14,000 units, approximately. 



46 



roper's catechism for 



TABLE 

OF TEMPEEATUEES EEQUIEED FOE THE IGNITION OF 
DIFFEEENT COMBUSTIBLE SUBSTANCES. 



Substances. 


Temperature 
of Ignition. 


Remarks. 


Phosphorus, 


140° 


Melts at 110°. 


Bisulphide of carbon vapor, 


300° 


Melts at 130°. 


Fuhuinatiijg powder, . . . 


374° 


Used in percussion caps. 


Fuhuiiiate of mercury, . . . 


392° 


According to Legue and 
Champion. 


Equal parts of chlorate of 
potash and sulphur, . . 




395° 




Sulphur, 


400° 


Melts, 280° ; boils, 850°. 


Gun-cotton, 


428° 


According to Legue and 
Champion. 


Nitro-glycerine, 


494° 


" " " 


Eifle-powder, 


550° 


" " " 


Gunpowder, coarse, .... 


563° 




Picrate of mercury, lead, or 






iron, 


565° 


11 ti <i 


Picrate powder for torpedoes, 


570° 


« « (( 


Picrate powder for muskets, 


576° 


« <( 11 


Charcoal, the most inflam- 






mable willow used for gun- 






powder, 


580° 


According to Pelouse 
and Fremy. 






Charcoal made by distilling 






wood at 500°, 


660° 


<( i< (< 


Charcoal made at 600°, . . . 


700° 


11 It (i 


Picrate powder for cannon, . 


716° 




Very dry wood, pine, . . . 


800° 




Very dry wood, oak, .... 


900° 




Charcoal made at 800°, . . . 


900° 





It will be seen by the above table that the most combust- 
ible substances, generally considered very dangerous, will 
only ignite by heat alone at a high temperature, so that for 
their prompt ignition it requires the actual contact of a 
spark. 



STEAM ENGINEERS AND ELECTRICIANS. 47 

Q. How many heat-miits does 1 pound of good 
coal, containing 90 per cent, of carbon, produce ? 

A. It produces in burning about 13,000 units. 

Q. What is the mechanical equivalent of 13,000 
units ? 

A. 10,114,000 foot-pounds, — that is to say, 
10,114,000 pounds raised 1 foot high. 

Q. How much air does it require to burn 1 
pound of coal? 

A. About 155 cubic feet. 

Q. How much air does it require to burn 100 
pounds of coal ? 

A. About 15,500 cubic feet of air. 

Q. What is the difference between anthracite 
and bituminous coal ? 

A. Anthracite coal is nearly all carbon, having 
only about 10 per cent, of other matter, while 
bituminous coal has from 15 to 50 per cent, of 
other materials besides pure carbon. 

Q. What is the relative fuel value of anthracite 
coal and wood ? 

A. A pound of coal is equal to about 2\ pounds 
of wood. 

Q. What is coke? 

A. Coke is what is left of coal after the volatile 
ingredients have been driven off by distillation, 
as in gasworks; or by partial combustion, as in 
coke-ovens. 



48 



ROPER S CATECHISM FOR 



TABLE 

SHOWING THE TOTAL HEAT OF COMBUSTION 

OF VARIOUS FUELS. 



Sort of Fuel. 



Equiva- 
lent in 
pure 
carbon. 



Evapora- 
tive power 
in lbs. water 
from 212° 
Fahr. 



Total heat of 

combustion 

in lbs. water 

heated 1° 

Fahr. 



Charcoal, 

Charred peat, 

Coke— good, 

Coke — mean, 

Coke — bad, 

Coal: 
Anthracite, ...,,... 
Hard bituminous — hardest, . 
Hard bituminous — softest, . 

Coking coal, 

Cannel coal, 

Long-flaming splint coal, . . 
Lignite, 

Peat: 

Perfectly air-dry, 

Containing 25 per cent, water. 

Wood : 

Perfectly air-dry, 

Containing 25 per cent, water, 



0.93 
0.80 
0.94 

0.88 
0.82 



1.05 
1.06 
0.95 
1.07 
1.04 
0.91 
0.81 



0.66 



0.50 



14.00 
12.00 
14 00 
13.20 
12.30 



15.75 
15.90 
15.25 
16.00 
15.60 
13.65 
12.15 



10.00 
7.75 



7.50 

5.80 



13,500 
11,600 
13,620 
12,760 
11,890 



15,225 
15,370 
13,775 
15,837 
15,080 
13,195 
11,745 



9,660 
7,000 



7,245 
5,600 



I 



Remark. — In a boiler of fair construction, a pound of 
coal will convert 9 pounds of water into steam. Each 
pound of this steam will represent an amount of energy, or 
capacity for performing work, equivalent to 746,666 foot- 
pounds, or for the whole 9 pounds, 6,720,000 foot-pounds. 
In other words, 1 pound of coal has done as much work in 
evaporating 9 pounds of water into 9 pounds of steam as 
would lift 300 tons 10 feet high. 



STEAM ENGINEERS AND ELECTRICIANS. 49 

Q. Next to carbon, which of the constituents of 
coal is the greatest heat producer ? 

A. Hydrogen. 

Q. What is the number of heat-units produced 
by burning a pound of hydrogen ? 

A. 62,000 British thermal units. 

Q. Why do some coals have a greater heat-pro- 
ducing value per pound than does pure carbon ? 

A. Because they are so rich in hydrogen. 

Q. What is meant by the term ' ' free hydrogen ' ' 
in connection with coal ? 

A. In all fuel containing carbon, hydrogen, and 
oxygen, the proportion of hydrogen may be equal 
to or greater, but never less, than that required to 
form .water with the oxj^gen. It is only the 
hydrogen in excess of this which is available as a 
source of heat, and this is called free hydrogen. 
The hydrogen existing in combination with oxygen 
in the state of water, so far from contributing to 
the actual amount of heat produced, must be 
, evaporated at the expense of the heat developed 
by the combustion of the carbon. 

Q. How does the heat-producing value of petro- 
leum compare with that of coal ? 

A. It is about ^ greater, pound for pound. 

Q. What are some of the advantages of using 
petroleum as a fuel ? 

A. It gives a steadier fire, is more easily hand- 
4 



50 roper's catechism for 

led, makes no ashes and little smoke, and does 
not take up so much space. 

Q. What determines the advisability of using 
petroleum rather than coal at a certain place ? 

A. The most important point is the relative '. 
cost of the two. 

Q. How many pounds of water can be evapo- 
rated by a pound of coal ? 

A. This depends upon the kind of boiler used 
and its condition, and also on the kind of coal, 
the amount varying from 6 to 12 pounds. Under 
most favorable conditions an evaporation of over 
13 pounds of water per pound of combustible 
has been secured. 

Q. What is the meaning of the term ' ' com- 
bustible ' ' used in connection with coal ; for 
example, in the expression, ' ' pounds of water 
evaporated per pound of combustible ? ' ' 

A. The amount of ' ' combustible " in a quantity 
of coal is found by subtracting from the original 
weight of the coal the weight of the water in the 
coal plus the weight of the ash produced when 
it is burned. 

AIR AND OTHER GASES. 

Q. What are the three most important element- 
ary gases — that is, the three most important 
elements existing naturally in the gaseous state ? 



STEAM ENGINEERS AND ELECTRICIANS. 51 

A. Oxygen, nitrogen, and hydrogen. 

Q. What are some of the most important char- 
acteristics of oxygen? 

A. It is colorless, tasteless, and odorless. It 
supports combustion, which process is the chemi- 
cal combination of the oxygen of the air with the 
burning substance. It is necessary for the respi- 
ration of animals and clearing the blood of im- 
purities. It combines readily with nearly all other 
chemical elements. 

Q. What is iron rust ? 

A. A combination of iron with oxygen, known 
as oxide of iron. 

Q. What relation does rusting bear to com- 
bustion ? 

A. Rusting is slow oxidation; combustion is 
rapid oxidation. 

Q. What are some of the characteristics of 
nitrogen ? 

A. It is also colorless, tasteless, and odorless. 
Unlike oxygen, it does not combine readily with 
other elements; it will not burn nor support com- 
bustion; mixed with oxygen it forms atmospheric 
air, its function being to dilute the oxygen. 

Q. Give some of the qualities of hydrogen. 

A. It is colorless and tasteless and odorless 
when pure. It is the lightest of known substances, 
being only one-sixteenth as heavy as air. It 



52 roper's catechism for 

unites most readily with oxygen, combining with 
it to form water in the proportion of 1 part by 
weight of hydrogen to 8 parts of oxygen. It 
burns in air with a bluish flame. 

Q. Of what does the atmosphere consist ? 

A. Of oxygen and nitrogen mixed together (not 
chemically combined), in the ratio of about 1 
part by volume of oxygen to 4 parts of nitrogen. 

Q. How far from the earth's surface is the 
atmosphere supposed to extend ? 

A. At least 45 miles. 

Q. Is its density uniform — that is, is it the 
same at different heights ? 

A. No; it is less dense as we go farther from 
the earth's surface. 

Q. Does air have any weight ? 

A. Yes; a cubic foot at the level of the sea 
weighs about yfo- of a pound. 

Q. What is atmospheric pressure, so-called ? 

A. It is the pressure exerted on all bodies by 
the air, owing to its weight. Since all gases trans- 
mit a pressure equally in all directions, and since 
air has weight, it follows that any square inch of 
surface has a pressure exerted on it equal to the 
weight of a column of air 1 square inch in cross- 
section and of 45 miles or more in length. 

Q. How much is this weight, or, in other words, 
how much is the atmospheric pressure? 



STEAM ENGINEERS AND ELECTRICIANS. 



53 



TABLE 

SHOWING APPROXIMATE INCREASE IN BULK OF 
DUE TO INCREASE OF TEMPERATURE, AT 
ATMOSPHERIC PRESSURE. 



Fahrenheit. 

Temp. 32 (Freezing-point) 

" 38 

" 34 

"35 .... 


Bulk Fah 
. 1000 Tei 

1002 

1004 

1007 

1009 

1012 

1015 

1018 
. 1021 

1023 
. 1025 

1027 

1030 
. 1032 ' 

1034 

1036 

1038 

1040 

1043 ' 

1045 

1047 

1050 

1052 

1055 ' 

1057 

1059 

1062 
. 1064 

1066 
. 1069 ' 
. 1071 

1073 

1075 

1077 

1080 

1082 

1084 

1087 

1089 

1091 

1093 

1095 

1097 


renheit. 

up 75 ... 




Bulk 
1099 


76 (Summer heat) . 

' 77 

' 78 


1101 
1104 
1106 


" 36 ... : 

" 37 


' 79 ... . 

' 80 ... . 




1108 
1110 


" 38 


' 81 . . . 




1112 


" 39 


' 82 ... . 




1114 


" 40 


'83 




1116 


«' 41 


' 84 ... . 




1118 


" 42 


' 85 ..." . 




1121 


"43 


' 86 




1123 


"44 .... 


' 87 




ll'?5 


" 45 


' 88 . . . 




1128 


"46 ... 


' 89 




1130 


" 47 


' 90 ... . 




1132 


" 48 


' 91 




1134 


" 49 


' 92 ... . 
' 93 . , . 




1136 


" 50 


1138 


"51 .... 


' 94 




1140 


" 52 

" 53 

" 54 


' 95 . 

' 96 (Blood heat) . . 

' 97 

' 98 


1142 
1144 
1146 


" 55 


1148 


" 56 (Temperate) . . 


' 99 ... . 




1150 


'100 ... 




1152 


" 58 


' 110 ... 




1173 


" 59 . . 


120 




1194 


" 60 


'130 ... 




1215 


" 61 


' 140 ... . 




1235 


" 62 

" 63 

" 64 

" 65 

" 66 


' 150. .. . 
' 160. .. . 
' 170 (Spirits 
' 180 ... . 
' 190 


boil', 176) 


r55 
1275 
1295 
1315 
1334 


" 67 


' 200 ... . 




1364 


" 68 


' 210 




1372 


'• 69 

" 70 


' 212 (Water 
' 302 


boils) . . 


1375 
1558 


" 71 


'392 ... 




1739 


" 72 

- •' 73 

" 74 


' 482 ... . 
' 572 ... . 
' 680 




1919 

2098 
2312 











54 roper's catechism for 

A. At sea-level and at 32° Fahr. it is about 14.7 
pounds per square inch, or, in round numbers, 
15 pounds. 

Q. What would you understand b}^ a pressure 
of three atmospheres ? 

A. A pressure of 45 pounds per square inch. 

Q. What instrument is used to measure atmos- 
pheric pressure ? 

A. The barometer. 

Q. How is it made ? 

A. By filling a glass tube about 3 feet long with 
mercury and then inverting the tube, letting its 
open end rest in a vessel containing mercury. 
The height of the top of the mercury column in 
the tube is read by a graduated scale. 

. Q. Why does the mercury not run entirely out 
of the tube into the vessel? 

A. The mercury column is acted upon by two 
forces; its weight tends to make it run out, but the 
atmosphere pressing on the surface of the mercury 
in the vessel resists this action. The mercury 
column in the tube, therefore, falls only to the 
point where the pressure per square inch due to 
the weight of the column is just equal to the 
pressure per square inch exerted by the atmos- 
phere. 

Q. Will the reading of the barometer on a 
mountain be higher or lower than at sea-level ? 



I 



STEAM ENGINEEES AND ELECTRICIANS. 55 

A. Lower; for the atmospheric pressure being 
less, it cannot balance so long a column of mer- 
cury. 

Q. Why does the mercury column of the 
barometer at a certain place stand at different 
heights at different times ? 

A. Owing to the presence of more or less water, 
vapor in the atmosphere which changes the weight 
per cubic foot of air, and consequently alters the 
atmospheric pressure. 

Q. How can the height of a place above sea- 
level be measured by the barometer ? 

A. By reading the barometer at the given place 
and comparing this reading with that taken at 
some known altitude. Roughly, each inch of 
length of the barometer column corresponds to a 
difference in level of 1000 feet. 

Q. Can heights also be measured by the ther- 
mometer ? 

A. Yes; by observing at what temperature 
water boils. At sea-level it boils at 212° Fahr. 
Roughly, for every 500 feet rise above sea-level 
the temperature of the boiling-point is 1 degree 
less.* 

Q. What is the effect of heat on air ? 

A. To expand it. 

*For more accurate calculations of heights, see "Roper's 
Engineers' Handy-Book," pages 121-134. 



66 roper's catechism for 

Q. What is the method of calculatmg this ex- 



pansion 



A. Under constant ^ pressure, for each degree 
Fahr. rise in temperature the volume of air ii 
increased by ^2" ^^ i^^ volume at 32° Fahr. 



WATER. 

Q. Of what is water composed ? 

A. Of the elementary gases, oxygen and hydro- 
gen, in the proportion by weight of 89 parts of 
oxygen to 11 parts of hydrogen. By volume the 
ratio is 1 part of oxygen to 2 parts of hydrogen. 

Q. Is pure water found in nature ? 

A. No; water has, in solution, oxygen, nitrogen, 
and ammonia, taken up from the air, and traces 
of salts of many minerals. It may also contain 
organic impurities resulting from the decomposi- 
tion of animal or vegetable matter. 

Q. Water is taken as the standard for specific 
gravity of liquids, but is its specific gravity 
always uniform ? 

A. No; the weight of a cubic foot of water 
depends upon its purity. The presence of any 
salts in solution makes it heavier as in the case of 
sea water. 

Q. Does the temperature of water have any 
effect upon its specific gravity ? 

A. Yes; at about 39.2° Fahr. pure water is at 



I 



STEAM ENGINEERS AND ELECTRICIANS. 57 

its greatest density, that is, weighs most per cubic 
foot. Above this temperature it is less dense; 
below this point it also becomes less dense until 
at 32° it solidifies into ice. 

Q. Under what conditions, then, is water taken 
as the standard for specific gravities ? 

A. With the understanding that the water is 
pure and is at a temperature of 39.2° Fahr. 

Q. In what three physical states or forms does 
water exist ? 

A. As ice, water, and steam. 

Q. How do the weights of a cubic foot of ice, 
water, and steam compare ? 

A. A cubic foot of ice weighs about 57 pounds; 
of water, about 62 J- pounds; and of steam, at 5 
pounds gauge pressure, yl-g- pounds, and at 100 
pounds gauge pressure, y^^-g- pounds. 

Q. What is necessary to change from one of 
these forms to the other? 

A. Merely the application or withdrawal of heat. 

Q. Is water a good conductor of heat ? 

A. No. 

Q. Is it a good conductor of electricity ? 

A. Not if reasonably pure. The addition of 
some soluble metallic salt, like sodium carbonate 
or of sulphuric acid, makes it a good electrical 
conductor. 
!l Q. What are some of its other properties ? 



58 eoper's catechism for 

A. It is tasteless, odorless, and colorless, and a 
solvent for most gases and a vast number of 
liquids and solids. 

Q. At what temperature does water boil ? 

A. This depends upon its purity and upon the 
atmospheric pressure. Reasonably pure water at 
the sea-level boils at 212° Fahr. 

Q. On a mountain 3000 feet above sea-level, at 
about what temperature would you expect water 
to boil? 

A. At about 206° Fahr., as for every 500 feet 
above sea-level the boiling-point drops approxi- 
mately 1 degree. 

Q. How does the boiling-point of salt water 
compare with that of fresh water ? 

A. It is higher. 

Q. Which will hold the greater quantity of a 
substance in solution, hot water or cold water? 

A. This depends on the nature of the substance. 
Salts of lime are less soluble in hot water and, 
therefore, if they exist in a natural water will be 
deposited when the water is heated to a high 
temperature. 

Q. How does the specific heat of water com-- 
pare with that of other substances ? flj 

A. It is greater than that of nearly all other^ 
and it is for this reason that it is chosen as tlie 
standard for specific heats. 



STEAM ENGINEERS AND ELECTRICIANS. 59 

Q. What is the specific heat of ice ? 

A. About .5, or half that of water. 

Q. How many units of heat are necessary for 
melting 1 pound of ice ? 

A. About 142. 

Q. How can water be decomposed into its con- 
stituents — oxygen and hydrogen ? 

A. By passing an electric current through it.* 

Q. Can we recombine these two gases to form 
water ? 

A. Yes; by burning the hydrogen in a jet in a 
vessel containing the oxygen. 

Q. What is the specific gravity or density of a 
body? 

A. Its weight per unit volume; and since the 
unit volume used by physicists is the cubic centi- 
meter the specific gravity or densitj^ is the weight 
(in grams) per cubic centimeter. 

Q. What would be the specific gravity of pure 
water ? 

A. 1, because the weight of a cubic centimeter 
of pure water is 1 gram. 

Q. What is taken as the standard of specific 
gravities ? 

A. Water, because its specific gravity is 1. 

Q. How could you obtain the specific gravity 
of any liquid ? 

*See "Roper's Engineers' Handy-Book." page 134. 



60 eoper's catechism for 

A. By weighing equal bulks of the. liquid and' 
of water and dividing the weight of the liquid by 
tlie weight of the water. 

Q. How could you obtain the specific gravity 
of a solid heavier than water ? 

A. Weigh it in air; place it in a jar even full 
of water and catch the overflow of water and 
weigh it. Divide the weight of the body in air 
by the weight of the water it displaces; the quo- 
tient will be the specific gravity. 

Q. When a body whose specific gravity is 
greater than 1, that is, greater than that of water, 
is placed in water, what occurs ? 

A. The body sinks. 

Q. How much water does it displace ? 

A. A volume in cubic feet or inches equal to 
the volume of the sinking body. 

Q. What happens if the specific gravity of the 
bod}^ is less than 1 ? 

A. The body floats, sinking only to a certain 
depth in the water. 

Q. How much water does it disi3lace ? 

A. Such an amount as will weigh the same as 
the floating body. 

Q. What is meant by the term "head " ajoplied 
to water? 

A. It means a difference in level ; for example, 
with a filled tank at the top of a house, the upper 



STEAM ENGINEERS AND ELECTRICIANS. 61 

level of the water in the tank being, say, 50 feet 
above the level of a spigot in the basement, there 
would be exerted at the spigot a pressure equal 
in pounds to the weight of a column of water 50 
feet high ; we should say, then, that there was at 
the spigot a head of 50 feet. 

Q. With a head of 100 feet, how would the 
.pressure compare with the preceding case ? 

A. It would be double, the pressure being 
strictly proportional to the head. 

Q. What pressure corresponds to a head of 1 
foot? 

A. Remembering that a cubic foot, or 1728 cubic 
inches, of water w^eighs 62.5 pounds, it is easily 
calculated. A column of water 12 inches high by 
1 inch square would contain 12 cubic inches and 
would weigh yyfg- or y^ of 62.5 pounds, or .43 
pound. Therefore, the pressure due to a head of 
1 foot would be .43 pound per square inch. 

Q. When water flows from an orifice in the 
bottom of a tank under a head, how can its velocity 
be calculated ? 

A. Were it not for friction of, and eddy currents 
in, the water at the orifice, each particle of water 
would emerge at a velocity the same as it would 
have if it were allowed to drop through a height 
equal to the head (the head in this case is the 
difference in level between the upper surface of 



62 roper's catechism for 

the water and the orifice). The formula is v = 
V 64. 4 h, or velocity in feet per second equals the 
square root of 64.4 X the head in feet. Owing 
to eddy currents set up at the orifice, the actual 
velocity will be slightly less than the value of v 
obtained from the formula. 

Q. Suppose that you desired to know the num- 
ber of cubic feet of water flowing from an orifice, 
how would you obtain it? 

A. First obtain, as above, the velocity in feet per 
second, multiply this by the area of the orifice in 
square feet, and multiply the product by ■^. The 
result will be the quantity in cubic feet per second. 

Q. Why do you multiply by ^^ ? 

A. Because the jet of water issuing from the 
orifice has an area less than that of the orifice, 
it being from six- to eight-tenths as large, accord- 
ing to the form of the orifice. 

Q. When water is led from a tank through a 
long pipe and then allowed to flow from the mouth 
of the pipe into the air, will the velocity be the 
same as calculated above ? 

A. No; it will be less, owing to the friction of 
the water against the walls of the pipe, which 
causes a loss of pressure or loss of head. 

Q. What does the loss of pressure depend on ? 

A. The length*of pipe, its diameter, and the 
smoothness of the interior. 



STEAM ENGINEERS AND ELECTRICIANS. 63 

Q. Is the loss of pressure greater as the pipe is 
longer ? 

A. Yes; the loss is strictly proportional to the 
length of pipe, the loss for a length of 200 feet 
being double that for 100 feet. 

Q. What effect does increasing the size of pipe 
have on the loss of pressure ? 

A. The larger the pipe the less the lost pressure. 
The loss of pressure is proportional to the length 
of the pipe and the square of the velocity, and 
inversely proportional to the diameter of the 
pipe.^ 

Q. Having these tables, how would you calcu- 
late the velocity at which water escapes from a 
pipe 500 feet long, the height of the water in the 
tank being 50 feet above the mouth of the 
pipe ? 

A. Calculate first the flow, assuming no loss 
owing to friction; then, with this flow, from the 
tables calculate the loss of head ; subtracting 
this head from 50 feet gives the effective head. 
Finally, using the effective head, calculate the 
velocity of flow. 

* For tables of the loss of pressure, see "Eoper's Engi- 
neers' Handy-Book," page 42. 



64 roper's catechism for 

STEAM. 

Q. What is steam ? 

A. Steam is the gaseous form of water produced 
by the application of heat sufficient to raise the 
temperature of the water to 212° Fahr. 

Q. What are the most prominent properties* 
possessed by steam ? 

A. First, its high expansive force; second, its 
property of condensation; third, its concealed or 
latent heat. 

Q. Is steam in itself invisible ? 

A. Yes; and it only becomes visible by loss of 
temperature, as when a jet is discharged into the 
open air, and is then seen in the form of vapor. 

Q. If a jet of steam flowing into the air gave a 
cloudy appearance close to the opening, what 
would you conclude? 

A. That the steam was very moist, — that is, that 
it was carrying along with it a large quantity of 
water in finely divided particles. 

Q. How is the condensation of steam effected ? 

A. By the lowering of its temperature. 

Q. What is the difference in volume between 
water and steam at a temperature of 212° 
Fahr. ? 

A. 1700; that is to say, any given quantity of 
water converted into steam at the pressure of the 



STEAM ENGINEERS AND ELECTRICIANS. 65 

atmosphere or 212° Fahr. will present a volume 
1700 times greater than its original bulk. 

Q. What is dry- saturated steam ? 

A. The vapor formed from water at a certain 
temperature and pressure and either remaining in 
contact with the water, or, if withdrawn from con- 
tact with the water, not subjected to any further 
heating. 

Q. What is superheated steam ? 

A. Dry-saturated steam not in contact with 
water and raised to a higher temperature than 
that at which it was formed. 

Q. How does ordinary steam differ from dry- 
saturated steam ? 

A. It has minute particles of water suspended 
in it. 

Q. Can steam be raised to a very high tempera- 
ture? 

A, Yes; steam can be heated to nearly a red 
heat, but not while it is held in contact with 
water. 

Q. Is steam at ordinary pressure hot enough to 
ignite wood ? 

A. Not without the intervention of some other 
substance, such as linseed oil, greasy rags, or iron 
turnings. 

Q. What do you understand by the term ' ' steam 
pressure " ? 
5 



66 roper's catechism for 

A. The elastic force which steam exerts in every 
direction. 

Q. What is the sensible heat of steam? 

A. The heat which goes to raise its temperature, 
as, for example, if water at 32° Fahr. has heat 
applied to it, its temperature will rise up to, but 
not above, 212° Fahr. The number of heat-units 
required to raise 1 pound of water from 32° Fahr. 
to any temperature is called the sensible heat cor- 
responding to that temperature. 

Q. A¥hat other name is given to the sensible 
heat ? 

A. The heat of the liquid or the heat in water. 

Q. What is latent heat? 

A. Heat which is not sensible to the touch nor 
indicated by the thermometer. 

Q. Is there more than one latent heat ? 

A. Yes; the latent heat of liquefaction, as, fo] 
example, the heat absorbed when ice melts into 
water; and the late^it heat of vaporization, or the 
heat absorbed when water is changed to steam. 

Q. How may the existence of latent heat be 
shown ? 

y1. If a thermometer be placed in a vessel con- 
taining water which is being heated, the reading 
of the thermometer increases as heat is applied 
till it reaches 212°, at which point the water 
boils. After this, although heat is continually 



I 



STEAM ENGINEERS AND ELECTEICIANS. 67 

applied, the thermometer goes no higher. This 
amount of heat which goes to change the physical 
state of water without changing its temperature 
is called latent heat. 

Q. What is the latent heat of vaporization of 
water ? 

A. The amount of heat needed to change a 
pound of water into steam. 

■ Q. What is the sum of the latent heat of vapor- 
ization and the heat of the liquid, at any tem- 
perature, called? 

A. The total heat corresponding to that tem- 
perature. 

■ Q. Is the total heat the same for all pressures ? 
A. At atmospheric pressure it is 1180, at 100 

pounds gauge pressure it is 1217, and at 135 
pounds it is 1223. ' 

Q. Does the elasticity of steam increase with 
an increase of temperature ? 

A. Yes, but not in the same ratio; because if 
steam is generated from water at a temperature 
which gives it the pressure of the atmosphere, an 
additional temperature of 38° will give it a pres- 
sure of 2 atmospheres, and a still further addition 
of 42° will give it a pressure of 4 atmospheres. 

Q. Do you know any simple formula connecting 
the pressure and temperature of saturated steam ? 

A. Experiments have been made from which 



b<5 roper's catechism for 

tables have been constructed, known as tables of 
the properties of steam, which give the relation 
between pressure and temperature.* 

Q. What is indicated by the ordinary steam 
gauge ? 

A. The pressure of the steam above the atmos- 
phere, — that is, the number of pounds by which 
it exceeds atmospheric pressure. 

Q. How would you get the total pressure of the 
steam, — that is, the number of pounds pressure- 
above zero ? 

A. By reading the barometer, calculating the 
number of pounds of atmospheric pressure corre- 
sponding to the barometer reading, and adding 
this to the reading of the steam gauge. 

Q. When a pound of steam is condensed to 
water, how much heat is given up to the surround- 
ing air? 

A. An amount of heat equal to the latent heat 
of steam at the temperature at which it is. 

Q. If afterward the water cools to a still lower 
temperature, how much heat is given off? 

A. The amount can be found by subtracting the 
heat of the liquid at the lower temperature from 
that corresponding to the upper temperature; the 
difference will be the number of units of heat 
given out per pound of cooling water. 

*See "Roper's Land and Marine Engines." 



STEAM ENGINEERS AND ELECTRICIANS. 69 

THE STEAM BOILER* 

Designing steam boilers is not within the 
province of the stationary engineer. It is his 
duty not to build boilers, but to operate them to 
the best advantage. Frequently, however, he is 
called upon to assist in the selection of the type of 
boiler for a given purpose, and in this he should 
remember that the three most important objects 
to be attained are safety, durability, and economy. 

To secure safety it is necessary that the boiler 
should be made of good material, with good work- 
manship. 

To secure durability the boiler ought to be con- 
structed so as to give the greatest facilities and 
easiest access for cleaning, repairing, and renewal 
of any of its parts. The boiler should also be so 
designed as to avoid unequal strains by expansion 
and contraction, as far as possible. 

In attempting to secure economy in the genera- 
tion of steam, it is necessary, first^ to secure perfect 
combustion of the fuel, so as to produce the great- 
est amount of heat; secondly^ to apply the heat in 
the very best manner to the boiler, so as to heat 
the water in the most rapid manner possible ; 
thirdly, to be very careful to prevent the heat from 
escaping by radiation or with the products of 
combustion. If these three conditions be com- 



70 roper's catechism for 

plied with, our arrangements will be of the most 
economical character. The evaporative efficiency 
of any boiler and furnace is to be measured by the 
amount of water evaporated by any given weight 
of fuel in a given time. Mere waste of fuel, how- 
ever, is not the only defect attendant upon an 
inferior construction of boiler and furnace. Where 
these are not of the best kind, they must be of 
larger size in order to do the required amount of 
work; the grate surface must be larger, and more 
air must be needlessly raised to a higher tempera- 
ture, thus carrying off a large amount of heat in 
the waste products of combustion; all of which 
involves increased outlay of capital and larger 
running expenses. 

Many of the defects of modern boilers might 
be attributed to the fact that some of the in- 
ventors or designers seem to be partly, if not 
totally, ignorant of the first principles of mechan- 
ical science, and to competition between boiler 
makers themselves, in their efforts to undersell 
each other; consequently they have to deceive 
purchasers and steam users by magnifying small 
l)oilers into large ones. Therefore, when the boiler 
comes to be tested, its evaporative powers are 
found to be lacking, the fuel has to be burned 
under a sharp draught, and instead of the best 
results the worst are obtained. 



STEAM ENGINEERS AND ELECTRICIANS. 71 

In regard to the metal of the boiler itself, it is a 
well-known fact that the thicker the iron is, and 
the poorer its conducting qualities, the greater will 
be the amount of heat that will be lost or wasted; 
when, by using a superior quality of iron, one 
whose tensile strength and conducting powers are 
both very great, we lessen the resistance to the 
passage of the heat from the furnace to the water 
and greatly increase the economy of the boiler. 
It is well known to engineers that there is a wide 
difference in the physical properties of different 
grades of iron and steel used in boiler construction. 
Some kinds of boiler plate have nearly double the 
tensile strength of others, and, consequently, to 
secure the same strength the latter would have to 
be made twice as thick as the former. This would 
involve the interposition of a more difficult path 
between the fire and the water, reducing the 
efficiency and producing a weaker boiler, because 
the thicker plate has been subjected to greater 
strains in the bending. Consequent^ the thinner 
plate, is by far the more advantageous. On the 
other hand, as the tensile strength of boiler plates 
increases, its ductility decreases, and, therefore, 
great care must be taken in selecting boiler mate- 
rials, to be sure that they possess not only tensile 
strength, but also ductility, otherwise the plates 
will be subjected to initial strains, and, further- 



72 roper's catechism for 

more, the boiler will not be sufficiently flexible to 
withstand the varying strains to which it is con- 
stantly subjected. For these reasons it has been 
fouiid that the best material for boilers is one which 
has a moderate tensile strength, 50,000 to 60,000 
pounds per square inch, and which will elongate 
20 to 25 per cent, before breaking and contract 50 
per cent, in cross-section at the point where rup- 
ture takes place. 

Every attempt to lessen the first cost of a 
boiler by diminishing the heating- and grate- 
surface is, to a certain extent, carrying out the 
principle of '' penny wise and pound foolish." 

An engine extra large for the work to be done 
causes a loss of fuel, while a boiler moderately 
larger than necessary to do the work is productive 
of economy in the use of fuel. A boiler taxed to 
its utmost capacity will evaporate, say, from 5 to 
6 pounds of water per pound of coal, while the 
same boiler might evaporate half the quantity of 
water at the rate of 8 to 10 pounds of water per 
pound of fuel. This is due partly to the fact that 
when the boiler is forced the heating surface is not 
sufficient to utilize all of the heat from the prod- 
ucts of combustion, and partly also to the excess 
of air above that necessary for combustion which 
passes through the grate and which is heated with- 
out producing any useful effect. 



STEAM ENGINEERS AND ELECTRICIANS. 73 

For instance, a locomotive boiler burning 10 
pounds of coal on each square foot of grate surface 
in an hour, will evaporate, say, 8 pounds of water 
for each pound of coal. The same boiler, running 
at a high speed, and burning 75 pounds of coal 
on each square foot of grate surface, will evaporate 
7 pounds of water for each pound of coal burned. 
Here is a vast difference in the total amount of 
evaporation, — each pound of coal produces less 
steam in the proportion of 9 to 7 pounds. 

On the other hand, increasing the size of boiler 
for a given evaporation must not be carried to 
excess, because beyond a certain limit there is no 
advantage to be derived and the increased first 
cost then becomes a waste in the other direction. 
There is a certain fixed relation between grate 
surface, heating surface, and quantity of water 
evaporated, in each type of boiler, which has been 
found in practice to be the most advantageous, 
and any material departure from this in either 
direction will impair the cost of operation.* 

A boiler may generate steam with great economy, 
but, owing to the steam being wasted by improper 
application to the engine, the result is unsatis- 
factory and the boiler unjustly blamed. On the 
other hand, a boiler that carries out water with its 

* For proportions of grate area, heating surface, etc. , see 
page 95 e^ seg-.; also, " Eoper's Handy-Book, " Chapter X. 



74 roper's catechism for 

steam may show a large evaporation, but the 
steam being wet, is almost useless in the engine; 
so that in judging the results of a steam-power 
plant, great care must be taken to examine closely 
into all of the conditions, before condemning either 
the boiler or the engine. 

In selecting a type of boiler for a given pur- 
pose, there are many circumstances to be taken 
into account. Generally speaking, the most im- 
portant considerations, as stated above, are safety, 
economy, and durability; of these, safety should 
alwa^^s be first considered, because there are no 
conditions under which human life and property 
are not at stake. Consequently, if a boiler is 
not safe, it is not fit for use under any circum- 
stances. The question of economy must be looked 
at in a different way. Generally speaking, that 
boiler is the most economical which evaporates the 
greatest amount of water with the least consump- 
tion of coal, but there may be conditions under 
which this is not the case; for example, in the coal- 
regions, where fuel is very inexpensive, a highly 
efficient boiler, which is of necessity more com- 
plex than one which is less so, might cost more to 
operate on account of the interest on the greater 
first cost and the cost of attendance than a simple 
fine or even a plain cylinder boiler; and it is a fact 
that the most efficient and therefore most expen- 



STEAM ENGINEERS AND ELECTRICIANS. 75 

sive boilers are not commonly nsecl where fuel is 
cheap. Similar considerations might lead to the 
selection of a less durable boiler. Suppose, for 
example, the case of a bridge to be built in some 
out-of-the-way locality, the work requiring but a 
short time and the cost of transportation large 
compared to the value of the boiler. Under these 
circumstances it would probably not pay to use a 
boiler of the highest grade, but preferably one 
which was merely safe and cheap, did not require 
much attention, cleaning, etc. , and need not neces- 
sarily be durable. Such conditions, however, are 
very uncommon and, generally speaking, the most 
efficient and durable boiler is the safest and the 



DIFFERENT TYPES— ADVANTAGES AND 
DISADVANTAGES. 

Q. How would you classify steam boilers ? 

A! Into cylindrical, flue, fire tubular, and water 
tubular. 

Q. What advantages does the plain cylinder 
boiler possess over other types ? 

A. It is simple, inexpensive, easy to clean and 
repair, and reasonably safe. 

Q. What are its disadvantages ? 

A. Its disadvantages are numerous and great. 
First, on account of its relatively small heating 



ROPER S CATECHISM FOR 




STEAM ENGINEERS AND ELECTRICIANS. il 

surface, it is very bulky, and, consequently, for a 
given evaporative capacity, the space it occupies 
lis much greater than in more modern types. 
Secondly, on account of the high temperature at 
Iwhich the gases escape from the stack, it wastes 
fuel, and for this reason it is the least economical 
type of boiler in existence. Thirdly^ it takes a 
very long time to raise steam. Fourthly, the 
scale formed in the bottom, where the heat is 
imost intense, makes a non-conducting stratum 
which soon renders that portion of the heating 
surface useless and causes the iron to burn at that 
oint. 

Q. Are plain cylinder boilers much used at the 
present time ? 

A. No; they have disappeared almost entirely, 
mainly on account of their inefficiency. They 
ire found occasionally in localities where the cost 
3f fuel is very low. 

Q. Name the principal varieties of flue boilers 
md briefly describe their characteristics. 

A. The Cornish, Lancashire, and Galloway 
3oilers are the principal varieties of flue boilers. 
[n the Cornish type an internal cylindrical flue 
extends the whole length of the boiler and the 
urnace is usually contained in the flue. , The 
l^ancashire boiler has two internal flues with a 
urnace in each, the two flues uniting into one 



78 



roper's catechism for 




STEAM ENGINEERS AND ELECTRICIANS. i\) 

behind the bridge wall. The Galloway is similar 
to the Lancashire, but has a number of conical 
tubes, called Galloway tubes, inside and across the 
flues, through which the water circulates. The 
furnaces are either within the flues or external.* 

Q. What are the relative advantages and dis- 
advantages of the above-named boilers ? 

A. The Cornish boiler has a greater heating 
surface than the plain cylindrical boiler, and it 
has the further advantage that that portion of the 
shell on which the scale is deposited, is the coolest 
instead of the hottest point. It has the disad- 
vantage that, for the same water capacity, it must 
have a greater diameter. 

The Lancashire boiler has the same advantages, 
and additionally the combustion is more complete 
than in the Cornish type, because the furnaces 
may be fired alternately and the smoke which 
would issue from the stack, if there were but one 
furnace, is to a great extent consumed by coming 
in contact with the products of .combustion from 
the other furnace. It also has the disadvantages, 
in common with the Cornish boiler, that its diam"- 
eter is greater and, further, the liability of the 
internal flue to collapse, both of which disadvan- 
tages it possesses to an even greater degree than 

* For description of flue boilers, see " Roper's Engineers' 
Handy-Book," pages 160-164. 



80 roper's catechism for 

the Cornish boiler. The liability of the flue to 
collapse, however, is not very great when the 
flues are properly stiffened or corrugated. 

The Galloway boiler, being virtually a modified 
Lancashire boiler, possesses all of its advantages; 
and, additionally, by virtue of the conical tubes, 
which are placed transversely in the flues, it has 
a greater heating surface and better circulation. 
Furthermore, the flues are much less liable to 
collapse. All of this is accomplished by the 
Galloway tubes. Of the three boilers mentioned 
the Galloway type is the safest and most econom- 
ical in the use of fuel. 

Q. What methods are employed to stiffen the 
flues of boilers and to provide for linear expan- 
sion and contraction ? 

A. This end was formerly accomplished by 
making the flues in short lengths and connecting 
them by /\-shaped rings, riveted on each section 
of flue. The stiffening of the flue alone is also 
accomplished by placing T-shaped rings within 
the flues, at intervals, and by the use of Galloway 
tubes. This, however, does not take care of ex- 
pansion and contraction. The best way of ac- 
complishing both ends is by corrugating the 
flue, which has the further advantage of increas- 
ing the heating surface without taking up any 
more space in the boiler. 



STEAM ENGINEERS AND ELECTRICIANS. 81 

Q. What is meant by fire-tube or tubular boil- 



ers 



? 



A. Fire-tube or tubular boilers are those in 
which the combustion gases pass, not only around 
the outside shell, but also through tubes which are 
surrounded by water. 

Q. In what respect do they differ from flue 
boilers ? 

A. In no essential feature, except that instead 
of one flue of large diameter there are a number 
of small flues or tubes. 

Q. What is the difference between internally 
and externally fired tubular boilers ? 

A. The internally fired type consists of an ex- 
ternal cylindrical shell containing a furnace ex- 
tending from the front of the boiler to a point 
about midway in the length of the boiler. From 
this point, and extending to the rear end of the 
boiler, there are a number of tubes which lead the 
gases of combustion to the back, whence they pass 
under the outside shell to the front and into the 
stack. In the externally fired type the tubes 
extend the whole length of the boiler, and the 
furnace is outside and under the front end of the' 
boiler. The products of combustion pass along 
the bottom of the shell to the back of the boiler, 
and then return through the tubes to the front 
where they enter the stack connection. From the 



82 



ROPER S CATECHISM FOR 




STEAM ENGINEERS AND ELECTRICIANS. 83 

course which the gases take, this latter type is 
frequently designated as ''Return Tubular."^ 

Q. What ad\^antages does a tubular boiler pos- 
sess over the cylinder and flue boilers ? 

A. The tubular takes up less room, generates 
steam more rapidly, and requires less fuel; more- 
over, tubes are less dangerous than flues, on ac- 
count of their small diameter and great strength. 

Q. Why are tubular boilers more economical 
than plain cylinder and flue boilers ? 

A. Because their heating surface is much greater, 
and consequently the greater portion of the heat 
contained in the combustion gases is imparted to 
the water. 

Q. What are their disadvantages as compared 
to the above-mentioned types ? Are they impor- 
tant? 

A. The disadvantages are that the first cost' is 
greater, and that they are more difficult to clean 
and repair, because they are less accessible. These 
disadvantages are unimportant compared to the 
great gain in economy, f 

Q. What may be said about the tubular boiler 
in regard to safety ? 

A. The tubular boiler is just as safe as the 
cylindrical boiler, and more so than the flue boiler, 

*See "Roper's Engineers' Handy-Book," pages 165-168. 
t For comparison with water-tube boilers, see next page. 



84 roper's catechism for 

because the parts subjected to internal pressure 
have the same strength, while those subjected to 
external pressure, being smaller in diameter, are 
much stronger. 

Q. What is a water- tube boiler? 

A. It is one in which the water circulates 
through a series of tubes, which are surrounded 
by the combustion gases. 

Q. What is the position of the tubes in this 
class of boilers ? 

A. Different makers place the tubes in different 
positions. In the most common type, such as 
the Babcock and Wilcox, Heine, Gill and Root, the 
tubes are inclined; in others, such as the Cahall, 
they are vertical, and occasionally the}^ may even 
be found curved spirally.* 

Q. What are the principal advantages of the 
water-tube boiler as compared with other types ? 

A. Its advantages are that it is safer, more eco- 
nomical, steams more rapidly, is easily repaired, 
more durable; its form may be adapted to almost 
any existing conditions, and it may be easily taken 
apart and transported. Its only disadvantages 
are that it is heavy and expensive. 

Q. Why is this type of boiler the most econom- 
ical in the use of fuel? 

* Descriptions of the different types in a comdeused form 
can be found in Babcock and Wilcox's "Steam." 



STEAM ENGINEERS AND ELECTRICIANS. 85 

A. Because it has an enormous amount of heat- 
ing surface, and because the metal which con- 
stitutes the heating surface is comparatively light; 
because the combustion is very thorough, and com- 
paratively little heat is contained in the escaping 
gases. 

Q. Why is it the safest? 

A. Because for a given rating the parts sub- 
jected to strain are of smaller diameter than in 
any other type, and, moreover, none are subjected 
to external pressure. Further, because it is so 
flexible that the whole structure accommodates 
itself to changes in temperature without causing 
undue strains. 

Q. AVhat would probably be the difference in 
an explosion of a water - tube and a fire - tube 
boiler ? 

A. Explosions occurring in fire -tube boilers 
usually wreck the entire boiler, and in some cases 
whole batteries have been known to explode as 
the result of a single defect in one of the shells, 
entailing great loss of life and property. In the 
water - tube type, while more or less serious 
explosions have occurred, it is very rare for any- 
thing more than a single tube or header to give 
way; this may be easily repaired and does not 
generally entail much loss. 

Q. Why is it durable ? 



ROPER'S CATECHISM FOR 




STEAM ENGINEERS AND ELECTRICIANS. 87 

A. Because it is easily accessible, and because, 
as already stated, it adapts itself to the varying 
expansion and contraction without producing 
undue strains; further, the circulation is good and 
consequently the temperature of the different 
parts is fairly uniform. 

Q. To what class do locomotive and marine 
boilers belong? 

A. They may be said to belong to the tubular 
type, but they have certain characteristics not 
embodied in the ordinary tubular boiler, Avhich 
really place them in separate classes by them- 
selves. 

Q. Give a brief description of a modern marine 
boiler. 

A. It usually consists of a short, circular shell 
of large diameter with an internal corrugated fur- 
nace. At the back of the furnace is a- chamber 
into which the gases pass from the furnace. This 
is called the back up-take. A similar chamber in 
the front, called the front up-take, connects with 
the stack. The tubes are placed above and around 
the furnace, and extend from the front to the back 
up-take. 

Q. What, then, is the essential difference be- 
tween a marine boiler and an internally fired 
tubular boiler? 

A. The principal difference is that while in the 



05 ROPER'S CATECHISM FOR 

ordinary internally fired tubular boiler the gases 
pass from the furnaces through tubes to the back 
and then along the outside to the front; in the 
marine boiler the gases do not pass around the 
outside at all, but go from the furnace directly 
into the back up-take, thence through the tubes 
to the front up-take and into the stack. 

Q. What conditions have brought about this 
design of boiler for marine purposes ? 

A. For marine purposes a boiler must be short, 
as otherwise it could not be set and operated in 
the available space; and it must be self-contained, 
because brick setting, on account of its great 
weight and the motion of the ship, would be out 
of the question. It must also make steam 
rapidly. 

Q. What pressure may be carried in modern 
marine boilers ? 

A. Upward of 200 pounds per square inch. 

Q. How many furnaces are generally used ? 

A. Boilers less than 9 feet in diameter usually 
have only one; those from 9 to 13 feet, two; over 
13 feet, three; and the largest, sometimes exceed- 
ing 15 feet in diameter, have four furnaces. 

Q. What is meant by a double-ended boiler? 

A. When the boilers are fired from the sides of 
the ship they are frequentl}^ placed back to back 
or are made double-ended — that is, they have fur- 



STEAM ENGINEERS AND ELECTRICIANS. 89 

naces at both ends, with a common or separate 
back up-takes. The latter arrangement is prefer- 
able, because if anything should happen to a 
tube in one end, this may be repaired without 
affecting the other half of the boiler. 

Q. What are the advantages and disadvantages 
of marine-type boilers ? 

A. They do not occupy much floor space, 
require no brick setting, have a large steaming 
capacity for a given size and weight, but they are 
not as economical in the use of fuel or as safe as 
the best types of land boilers. 

Q. Are marine-type boilers ever used for sta- 
tionary purposes ? 

A. The marine type of boiler is occasionally 
found on land. It is well adapted for use where 
the vibration is so great as to render brick setting 
impracticable, and where floor space is limited. 

Q. Give a brief description of a locomotive 
boiler. 

A. The locomotive boiler consists of a rectang- 
ular furnace or fire-box, often made of copper, 
which contains the grate bars. The fire-box is 
inclosed in the boiler shell, which is also rec- 
tangular where it contains the fire-box, but the 
remainder of the shell consists of a long cylinder 
of comparatively small diameter, which contains 
a large number of tubes. The products of com- 



90 roper's catecpiism for 

bustion first strike a fire-brick arch which deflects 
them into the tubes, through which they pass 
into the funnel or stack placed on the smoke-box 
at the front end. Locomotives generally use 
forced draught, which is obtained by allowing the 
steam from the engine cylinders to exhaust through 
the funnel. 

Q. What conditions have led to the design now 
generally used for locomotive boilers ? 

A. A boiler suitable for use on locomotives 
must be light and of small diameter ; light, 
because it is carried along at a high rate of speed, 
and of small diameter on account of the limited 
width of the road bed. For the same reasons, 
and on account of the jarring motion, brick set- 
ting is out of the question, and hence it must be 
self-contained. It must be capable of making 
high-pressure steam quickly rather than econom- 
ically. 

Q. Is the locomotive boiler economical in the 
use of fuel ? 

A. Yes, but not as economical as the better 
types of stationary boilers. 

Q. How is the necessary strength of the flat 
surfaces of the fire-boxes obtained in locomotives? 

A. By short stay-bolts connected to the outside 
shell of the boiler. The top of the fire-box is 
sometimes braced by girders called crown-bars, 



STEAM ENGINEERS AND ELECTRICIANS. 91 

a;nd sometimes to the semi-circular shell of the 
boiler above by means of stay-bolts placed radially. 

Q. What are the advantages and disadvantages 
of the locomotive type of boiler ? 

A. Its advantages are that it is compact, steams 
quickly, and requires no brick setting. Its dis- 
advantages are that it is expensive, not as eco- 
nomical as the best stationary boilers, and is inac- 
cessible for cleaning and repairs. 

Q. Are locomotive-type boilers used for station- 
ary purposes ? 

A. Yes; they are well adapted for stationary 
boilers where head room is limited, where it is 
desired to make steam quickl}^ rather than eco- 
nomically, and where vibration or other condi- 
tions would make brick setting undesirable. 

Q. How is steam taken from locomotive boilers? 

A. Usually from a steam dome placed on the top 
of the shell. This is to insure dry-steam. Dry- 
pipes are also sometimes used instead of domes. 

HOESE-POWER AND EFFICIENCY. 

Q. What is meant by the term horse-poiver as 
applied to steam boilers ? 

A. A boiler of one horse-power capacity is one 
which, under ordinary conditions, supplies as 
much steam as is consumed in the average steam 
engine in developing one horse-power. 



92 eoper's catechism for 

Q. Is there nothing more definite than this by 
which the horse-power of boilers may be rated ? 

A. Yes; the horse-power of steam boilers is now 
generally based on an evaporative capacity of 30 
pounds of water per hour from feed-water at a 
temperature of 100° Fahr. to steam at a pressure 
of 70 pounds. This was fixed by a committee of 
judges at the Centennial Exposition in 1876, and 
is equivalent to 33,305 heat-units per hour im- 
parted to the water. It is known as the Centen- 
nial Rating. 

Q. How nearly does the horse-power of steam 
boilers, rated according to this rule, come to the 
actual consumption of steam in ordinary steam 
engines ? 

A. For an automatic cut-off, high-speed, non- 
condensing steam engine it is just about right. 
For plain slide-valve engines with throttling 
governors the Centennial Rating is much too low, 
while for multiple expansion and condensing 
engines it is too high. 

Q. How, then, would you fix the size of boilers 
for different engines, assuming that the horse- 
power of the boilers were based on the Centennial 
Rating? 

A. It is always well to have the boiler capacity 
a little in excess of that of the engine, because its 
efficiency is not impaired by operating it below 



STEAM ENGINEERS AND ELECTRICIANS. 93 

its rated capacity. If the engine were of the high- 
speed, automatic cut-off, single-expansion, non- 
condensing type, I should rate the boiler about 
10 per cent, higher than the engine; if of the 
same type, but condensing, about equal; if plain 
slide valve, non-condensing, with throttling gov- 
ernor, 40 to 50 per cent, higher; the same, con- 
densing, 10 to 20 per cent, higher; if automatic or 
four- valve non-condensing, about equal; the same, 
condensing, about 10 to 20 per cent, lower; if com- 
pound, high-speed, non-condensing, about 10 per 
cent, lower; the same, condensing, 15 to 25 per 
cent, lower ; if compound, four- valve, or Corliss, 
non-condensing, 10 to 15 per cent, lower; the same, 
condensing, 25 to 35 per cent, lower; if triple ex- 
pansion, non-condensing, 10 to 15 per cent, lower; 
the same, condensing, 35 to 45 per cent, lower. 

Q. Why are the above rules only approximate ? 

A. Because the evaporative capacity of a boiler 
depends on the temperature of the feed-water and 
also on the pressure of the steam. A boiler of 
100 ' horse-power can evaporate 3000 pounds of 
water from 100° to steam at 70 pounds pressure; 
but if the temperature of the feed-water is less, or 
if the pressure greater, it will not evaporate as 
much, and vice versa. 

Q. What, then, is the best method of determin- 
ing the size of a steam boiler ? 



94 roper's catechism for 

A. The best method is to determme what amount 
of steam is to be consumed and the pressure at 
which it is to be dehvered to the engine, to specify 
these requirements and the desired evaporative 
efficiency to the boiler-maker, and to leave the de- 
tails of construction to him, binding him to guar- 
antee the boiler to furnish the requisite amount of 
steam easily and under all conditions. 

Q. Approximately, what horse-power of boiler 
(Centennial Rating) would be required to supply 
steam to a 100 horse-power, four-valve, non-con- 
densing engine, consuming 26 pounds of steam 
at 70 pounds pressure per horse-power per hour ? 

A. Weight of steam required = 100 X 26 ^ 
2600 pounds per hour; H. P. (Centennial Rating) = 

-— — := 87, but it would probably be better to use 

a boiler rated at 90 to 100 horse-power. 

Q. What is meant by evaporative efficiency ? 

A. The number of pounds of steam generated 
per pound of fuel consumed. 

Q. What, roughl}^, are the results that may be 
obtained in this respect ? 

A. In flue boilers of the best types, 6 to 9 pounds; 
in tubular boilers, 8 to 10 pounds; in water- tube 
boilers, 10 to 12 pounds of water per pound of coal; 
the average results, however, are from 10 to 25 
per cent, below these figures. 



STEAM ENGINEERS AND ELECTRICIANS. 95 

GRATE AREA AND HEATING SURFACE. 

Q. What determines the grate surface m boilers ? 

A. Principally the quality of coal and the 
draught. In general, it is well to have the grate 
surface large, but not so large that the air passing 
through it will be greatly in excess of the amount 
required for combustion of the fuel. 

Q. What amounts of coal can be consumed per 
square foot of grate surface ? 

A. Anywhere from 4 to 120 pounds, depending, 
as already stated, upon the quality of the coal and 
the draught. 

Q. What is meant by heating surface ? 

A. The heating surface of a boiler means the 
aggregate area of all of the parts of the boiler which 
come in contact with the flame or products of 
combustion on the one side, and with the water 
or steam on the other. In other words, it is all 
that part of the surface through which the heat of 
the fire is transmitted to the water or steam. 

Q. How would you calculate the heating sur- 
face of different types of boilers ? 

A. Rule for Cylinder-Boilers. — Multiply f 
of the circumference of the shell in inches by its 
length in inches, add the area of one end in square 
inches, and divide by 144. The quotient will be 
the number of square feet of heating surface. 



96 roper's catechism for 

Rule for Flue-Boilers. — Multiply f of the 
circumference of the shell in inches by its length 
in inches;* multiply the combined circumference 
of all the flues in inches by their length in inches. 
Take the sum of these two products and add the 
area of one end in square inches. Deduct the 
sum of the areas of the cross-sections of all the 
flues in square inches. The result divided by 
144 is the heating surface in square feet. 

Rule for Vertical Tubular Boilers (such as 
are generally used for fire-engines). — Multiply the 
circumference of the fire-box in inches by its 
height above the grate in inches. Multiply the 
combined circumference of all the tubes in inches 
by their length in inches, and to these two prod- 
ucts add the area of the lower tube- or crown- 
sheet, and from this sum subtract the area of all 
the tubes, and divide by 144. The quotient will 
be the number of square feet of heating surface in 
the boiler. 

Rule for Horizontal Tubular Boilers. — 
Multiply f of the circumference of the shell in 
inches by its length in inches; multiply the com- 
bined circumference of all the tubes in inches by 
their length in inches. To the sum of these two 
products add f the area of both tube-sheets; from 
this sum subtract the combined area of all the 
tubes ; divide the remainder by 144, and the 






STEAM ENGINEERS AND ELECTRICIANS. 97 

quotient will be the number of square feet of 
heating surface. 

Rule for Locomotive Boilers. — Multiply the 
length of the furnace-plates in inches by their 
height above the grate in inches; multiply the 
width of the ends in inches by their height in 
inches; multiply the length of the crown-sheet in 
inches by its width in inches; also the combined 
circumference of all the tubes in inches by their 
length in inches; from the sum of these four 
products substract the combined area of all the 
tubes and the fire-door; divide the remainder by 
144, and the quotient will be the number of 
square feet of heating surface. 

Q. How much heating surface per horse-power 
should be provided in fire- and water- tube boilers ? 

A. About 12 to 15 square feet. 

Q. How, then, can you approximate the horse- 
power of a given boiler ? 

A. By calculating the heating surface in square 
feet and dividing it by 14. 

Q. What is the average ratio between grate and 
heating surface in stationary boilers ? 

A. The average is about 35 feet of heating sur- 
face to 1 square foot of grate surface. This is for 
good anthracite coal, but for poorer grades the 
proportionate surface of the grate should be 
larger. 
7 



98 roper's catechism for 

Q. How much coal, of good anthracite quality, 
can be consumed per square foot of grate under 
ordinary conditions? 
A. About 11 pounds. 

Q. According to these figures, how much coal, 
on an average, would be consumed per horse-^DOwer 
per hour ? 

A. Heating surface per H. P., = 12 sq. ft. 

Grate " " := |- 1. " 

Coal consumption per sq. ft. of 

grate per hour, =11 lbs. 

Coal consumption per H. P. per 

hour, :^ ^ X 11 = 3f lbs. 

Q. If all the heat in the fuel were utilized in 
making steam, what would be the smallest theo- 
retical amount of good anthracite coal consumed 
per hour ? 

A. Heat-units required per 

H. P. (Cent'l R'g), = 33,305 
Heat-units in best an- 
thracite coal, = 14,000 
Minimum consumption 

per H. P. per hour, = fll^l" = 2.4 lbs. 

BOILER SHELLS. 

Q. What materials are used for boiler shells ? 
A. Wrought iron and steel. The latter is rap- 
idly replacing the former as a boiler material. 



STEAM ENGINEERS AND ELECTRICIANS. 99 

Q. Why is steel preferred ? 

A. Because for a given strength it is hghter ; 
and, as a thinner plate may be used, the efficiency 
of the heating surface is greater. 

Q. What thickness of boiler plate do you con- 
sider the safest, most durable, and economical for 
boilers ? 

A. First, to insure safety in shells and flues of 
boilers; the thickness proper to use depends very 
much on the quality of the iron, diameter of 
boiler, and pressure to be carried. Secondly, as to 
durability, the thickest iron is not always the 
best, as the outside of the sheet becomes burned 
and crystallized, and in most cases gives less wear 
and satisfaction than a thinner gauge. Thirdly, 
as to economy, thin boilers are more economical 
with fuel, and wear longer, provided in all cases 
that the diameter and the pressure are in propor- 
tion. 

Q. What would you consider the proper thick- 
ness for boilers ? 

A. The thickness of boiler iron or steel should 
range between f and y\- of an inch, for the rea- 
son that plates of greater thickness than f of an 
inch are liable to burn, especially if the circula- 
tion is poor, and they are difficult to work and 
rivet. If the plates are less than y\ of an inch 
thick, they cannot be properly caulked, and they 



100 roper's catechjsm for 

are liable to waste away by corrosion so as to 
impair the safety of the boiler. 

Q. What properties should be possessed by 
materials used for boiler plates ? 

A. Whether iron or steel, the test-piece should 
have a tensile strength of not less than 50,000 
pounds per square inch ; it should elongate 25 
per cent, in 8 inches before breaking, and should 
contract 50 per cent, in cross-section at the point 
where rupture takes place. It should stand bend- 
ing without injury around a radius equal to the 
thickness of the 23late. 

Q. Is the pressure the same on all riveted seams 
in boiler shells ? 

A. No; the pressure on the longitudinal rivets 
is nearly double that on the curvilinear rivets. 

Q. What do you mean by longitudinal and cur- 
vilinear rivets ? 

A. By longitudinal rivets I mean those that run 
lengthwise on the boiler; the curvilinear are those 
that are around the circumference of the shell. 

Q. If the pressure on the longitudinal seams is 
double that on the curvilinear, how can all parts 
of the boiler sustain the same pressure? 

A. By making the longitudinal seams double 
riveted and the curvilinear single. 

Q. What is the difference in strength between 
single- and double-riveted seams? 



STEAM ENGINEERS AND ELECTRICIANS. lOl 

A. Single-rivetecl seams are equal to about 56 
per cent, of the material used, while double rivet- 
ing is equal to about 70 per cent. 

Q. What do you mean by ' ' equal to about 
56 per cent, of material used ' ' ? 

A. I mean that the boiler plates lose 44 per 
cent, of their strength in the process of riveting. 

Q. What do you consider the proper diameter 
for rivets of boilers ? 

A. That would depend very much on the diam- 
eter of the boiler, thickness of iron, and pressure 
to be carried. For boilers from 36 to 42 inches 
diameter, and f iron, if single riveted, the rivets 
ought to be f of an inch for curvilinear, and f for 
the longitudinal; if double riveted, f will answer 
for both longitudinal and • curvilinear seams. 
From -f-Q iron down to y\ smaller rivets will 
answer. 

Q. Which do you consider the best method of 
riveting boilers,' by hand or by machine ? 

A. For average or thin boiler plates, hand 
riveting does very well, but for heavy iron, ^^g- or 
J inch thick, machine work is far superior; the 
power of the machine brings the work together 
better and with less injury to the iron than can be 
done by hand. 

Q. How should the fiber of the iron be placed 
to give the greatest strength ? 



102 roper's catechism for 

A. The direction in which the iron is rolled 
should always be placed around the boiler, and 
not lengthwise, because in cylindrical boilers the 
strain in the line of the axis is much less than the 
circumferential bursting strain. 

Q. Do you consider it an advantage to drill the 
rivet-holes in boilers instead of punching ? 

A. Yes; for all first-class work there can be no 
doubt but that all the rivet-holes ought to be 
drilled, on account of the liability of the plates 
to become fractured by the process of punching, 
causing a great reduction in the strength of the 
boilers. 

Q. Do you consider the use of the drift-pin 
ought' to be dispensed with as much as possible in 
making boilers ? 

A. Yes; a reckless use of the drift-pin has in 
many cases resulted in great injury to the boiler 
plates; and there is good reason to believe that 
such injuries as are caused by the drift-pin often 
hasten the destruction of the boiler. 

Q. What is a drift-pin ? 

A. It is a tapering steel pin introduced into the 
holes in the seams, to bring them into line. 

Q. How do you propose to dispense with the 
use of the drift-pin? 

A. If the holes are laid off carefully in the 
sheet, and punched with judgment, there will be 



STEAM ENGINEERS AND ELECTRICIANS. 103 

very little need for the clrift-pin, as the holes can 
be straightened by a flat reamer. Such work will 
be greatly superior to that where the drift-pin is 
used. 

Q. Do you think i^ would be of any benefit to 
slightly heat the boiler plates before rolling them 
to form the shell of the boiler? 

A. Yes; I think it would add very materially 
to the strength and durability of boilers if the 
sheets were rolled while warm, as the fiber of the 
iron would be drawn out; while, in the common 
practice of cold rolling, the fiber is crushed and 
broken. 

Q. Does hammering improve the quality of 
iron ? 

A. No; it only hardens it, but at the same time 
renders it more brittle, while rolling imparts 
toughness. 

Q. What fact is observable when boiler iron is 
broken suddenly, as in the case of steam-boiler 
explosions ? 

A. It generally presents a crystalline fractured 
appearance; when, if broken by some slow pro- 
cess, it presents a fibrous or silky appearance, — 
in the first case the fiber is fractured, and in the 
other it is drawn out. 

Q. What does the crystalline fracture indicate ? 

A. It indicates hardness, while a fibrous fracture 



104 roper's catechism for 

is a mark of softness and ductility. The finer and 
more uniform the crystals, the higher the qualit}^ 
of the iron. 

Q. Is the pressure equal on all sides of the shell 
of a boiler when under steam ? 

A. No; there is more pressure on the lower than 
on the upper side of a boiler; as the steam presses 
equally on the surface of the water as on the upper 
side of the boiler, the weight of the water must 
be added to the pressure on the lower side. 

Q. Are the shells and flues of boilers sometimes 
injured by the application of the cold-water or 
' ' hydrostatic ' ' test ? 

A. Yes; the shells and flues of boilers are some- 
times injured by a reckless use of the test, and in 
many cases explosions take place soon after the 
test is applied. 

Q. Would the shell and flues of a boiler be 
stronger under a cold-water pressure of 70 or 80 
pounds to the square inch than under the same 
steam pressure ? 

A. No; as iron increases in strength by the 
application of heat up to 550° Fahr., the boiler 
would be stronger under the steam pressure. 

Q. How do you calculate the bursting pressure 
per square inch of a C3dindrical boiler? 

A. The rule is to multiply the thickness of the 
shell in inches by the tensile strength of the 



STEAM ENGINEERS AND ELECTRICIANS. 105 

material in pounds per square inch, and divide 
the product by one-half the diameter of the boiler 
in inches. 

Q. How do you calculate the safe working 
pressure ? 

A. Multiply the thickness of the shell in inches 
by the tensile strength in pounds per square inch. 
Multiply one-half the diameter by the factor of 
safety. Divide the first product by the second, 
and the quotient will be the safe working pressure. 

Q. What is meant by the factor of safety ? 

A. By factor of safety is meant the ratio of the 
ultimate breaking strength to the proper allowable 
working strength. For example, if a boiler shell 
is made of steel having a tensile strength of 
60,000 pounds and the thickness is calculated with 
a factor of safety of 4, the greatest strain which 
would come on any square inch of cross-section 
is 15,000 pounds; or, in other words, the boiler 
could carry four times as much pressure before 
bursting. 

Q. What is the factor of safety usually em- 
ployed in designing boiler shells ? 

A. It varies from 3 to 5. A safe average for 
stationary boilers is 4. 

Q. What value of tensile strength must be used 
in the above rules for working and bursting pres- 
sure ? 



106 



ROPER S CATECHISM FOR 



A. That depends on how the joints are riveted. 
The value of tensile strength in the above rules is 
the ultimate breaking strength of the material 
multiplied by the efficiency of the joint. 

Q. What do you mean by the efficiency of the 
joint ? 

A. I mean the number by which the original 
strength of the material must be multiplied to 
give its strength after riveting. 



t(S> O O (9 Q O ID , 




Q. What is the efficiency of single- and double- 
riveted joints ? 

A. As already stated above, it is about j^-^-q for 
single-riveted and about -^q- for double-riveted 
joints. The efficiencies of joints depend, how- 
ever, not only on the thickness of j^late, but also 
on the spacing of the rivets and the material used. 



STEAM ENGINEERS AND ELECTRICIANS. 107 

Q. How would you express by formulae the 
relations existing between safe working pressure, 
bursting pressure, thickness of shell, efficiency of 
joint, and factor of safety ? 

A. If p is the safe working pressure in pounds 
per square inch, 
P " bursting pressure in pounds per 

square inch, 
W " ultimate tensile strength in 

pounds per square inch, 
t ' ' thickness of shell in inches, 
e " efficiency of the joint, 
/ " factor of safety, 
d ' ' diameter of boiler in inches. 
To find the bursting pressure: 
j,_ t X WX e 
id ' 
To find the safe working pressure : 
_tXWXe 
^~ idXf ' 
To find the thickness of shell for a given work- 
ing pressure and factor of safety: 
_ i^ XpXf 
WX e ' 
To find the factor of safet}^ of a given boiler: 
f =, WX e X t 



108 eoper's catechism for 

Q. As an example: If a boiler 48 inches in 
diameter is made of steel having an ultimate ten- 
sile strength of 55,000 pounds per square inch, 
thickness of shell f of an inch, joints double 
riveted, what is the bursting pressure ? 

, r> I X 55,000 X .70 ^„„^ , 

A. P = :r-^ — -i^ = 1000 pounds 

i X 48 ^ 

per square inch. 

Q. With a factor of safety of 5, what would be 
the safe working pressure ? 

, f X 55,000 X .70 ^„„ , 

A. p= -r x-4^^^ = 200 pounds 

per square inch. 

Q. If the boiler had to work under 150 pounds 
pressure with a factor of safety of 4, what would 
be the proper thickness of shell ? 

. ^ 1 X 48 X 150 X 4 3 „ . , 

A. t = 55^000 X. 70 ^ * "^ ^"^ ^^^'^- 

Q. If a boiler of the same diameter were made 
of wrought, iron having an ultimate tensile 
strength of 50,000 pounds, shell \ inch thick, 
joints single riveted, what would be the factor of 
safety for a working pressure of 100 pounds ? 

, ^__ 50,000 X .56 X4 _^^^ 

^' ^- iX48x 100 -^'^^^ 

which is somewhat higher than is usually allowed 
by boiler makers. 



STEAM E^-GINEERS AND ELECTRICIANS. 109 

BOILER SETTING. 

Q. What materials should be used for settmg 
boilers ? 

A. The walls should be of hard burned brick 
laid in Portland cement. They should be of 
ample thickness so as to prevent loss by radiation. 
All surfaces exposed to the action of the hot gases 
should be lined with best quality fire-brick laid in 
a thin mortar of fire-clay. 

Q. What should be the course of the gases in 
a tubular boiler ? 

A. It should be set in such a way that the gases 
do not pass over the top of the boiler, unless there 
is ample space for a man to enter and clean off 
soot. 

Q. What should be the distance between the 
grate bars and the bottom of the boiler shell ? 

A. Not less than 24 inches. In large boilers it 
may be as much as 30 inches. 

Q. What should be the distance between the 
back tube sheet and rear wall ? 

A. From 18 inches for a 48-inch shell to 24 
inches for a 72-inch shell. 

Q. What is the best method of holding boiler 
walls in place? 

A. With the aid of buck-staves. 

Q. What are buck-staves ? 



110 roper's catechism for 

A. Vertical cast- or wrought-iron braces placed 
on the outside of the boiler walls, held together at 
the top and bottom by tie-rods. Buck-staves are 
often made of rails, flattened at the end to take 
the tie-rods. 

Q. How should the front of boilers be inclosed ? 

A. The best method is by a full flush front, 
which consists of cast-iron plates covering the 
entire front of the setting, leaving no brickwork 
in sight. The half-arch front which covers only 
the furnace is cheaper but less desirable. 

Q. When a number of boilers are set together, 
Avhat plan should be adopted ? 

A. Each boiler should be set independently of 
the others, and each should have a separate con- 
nection to the stack. 

Q. Why is this arrangement better than the 
old way of setting them in batteries, with a com- 
mon flue connection ? 

A. Because each boiler can be operated and shut 
down independently of the others; because the 
draught of one is not affected by the others; and, 
finally, because with the old method of setting, it 
often happened that when one shell gave out the 
whole battery exploded. 

Q. What kind of boiler should be used where 
excessive vibration exists or where brickwork 
would be too heavy ? 



STEAM ENGINEERS AND ELECTRICIANS. Ill 

A. A locomotive- or marine-type boiler is fre- 
quently used under these circumstances, because 

they require no brickwork whatever. 

f 

CARE AND MANAGEMENT. 

Q. What is the first duty of an engineer when 
he takes charge of an engine and boiler ? 

A. It is his duty to examine his boiler and see 
that the water is at the proper level. 

Q. How much water should the boiler contain 
when in use ? 

A. The water should be kept up to the second 
gauge while working, and up to the third at night. 

Q. Why should the level of the water be raised 
at night ? 

A. As a precaution against the water becoming 
too low from leakage or evaporation. 

Q. In case the water should become dangerously 
low, what would be the duty of the engineer ? 

A. He should immediately draw the fire and 
allow the boiler to cool, and not admit any cold 
water to the boiler or attempt to raise the safety 
valve, as it would be positively dangerous. 

Q. Why would it be dangerous to raise the 
safety valve ? 

A. Because it would lessen the pressure in 
allowing the steam to escape from the boiler, thus 
permitting the water to rise up and come in con- 



112 roper's catechism for 

tact with the overheated iron, and probably cause 
an explosion. 

Q. In case the water-supply should be cut off 
from the boiler for a short time, what w^ould be 
the duty of the engineer ? 

A. He should cover his fire with fresh fuel, stop 
his engine, and keep the regular quantity of w^ater 
in the boiler until the accident is repaired and the 
water-supply renewed. 

Q. How should an engineer proceed to get up 
steam ? 

A. He should first see that the water is at the 
proper level; he should then remove all ashes and 
cinders from the furnace, and cover the grate with 
a thin layer of coal; and after placing wood and 
shavings on the coal, he will be ready to start the 
fire. 

Q. What advantage is it to place a covering of 
coal on the grate before the wood or shavings ? 

A. It is a saving of fuel, as the heat that would 
be transmitted to the bars is absorbed by the coal, 
and the bars are also protected from the extreme 
heat of the fresh fire. 

Q, Should an engineer allow his fire to burn 
gradually when he commences to get up steam 
from cold water ? 

A. Yes; as by allowing the fuel to burn very 
rapidly, some parts of the boiler become expanded 



STEAM ENGINEERS AND ELECTRICIANS. 113 

to their utmost limits, while other parts are nearl}^ 
cold. Of course, a great deal depends upon the 
time in which he has to raise steam. 

Q. How should an engineer regulate his fire ? 

A. He should always keep the fire at a uniform 
thickness, and not allow any bare places or accu- 
mulations of ashes or dead coals in the corners of 
the furnace, as these places admit great qviantities 
of cold air into the furnace and render the com- 
bustion very imperfect. 

Q. Should an engineer avoid excessive firing as 
much as possible? 

A. Yes; as excessive firing is always attended 
with more or less danger, because the intense heat 
repels the water from the surface of the iron and 
allows the boiler to be burned. 

Q. How thick should an engineer keep his fires ? 

A. About 3 inches for anthracite coal and about 
5 inches for soft coal; but he should regulate the 
thickness of the fire according to the capacity of 
the boiler; if the boiler is too small for the engine, 
the fire should 'be kept thin, the coal supplied in 
small C[uantities and distributed evenly over the 
grate, and the grate kept as free as possible from 
ashes and cinders; but if the boiler is extra large 
for the engine, the thickness of the fire makes but 
little difference. 

Q. What should an engineer do in case, from 



114 roper's catechism for 

neglect or any other cause, his fire should become 
very low ? 

A. He should neither poke nor disturb it, as 
that would have a tendency to put it entirely out, 
but he should place shavings, sawdust, wood, or 
greasy waste on the bare places, with a thin cover- 
ing of coal; then by opening the draught to its 
full extent the fire will soon come up. If it 
should become necessary to burn wood on a coal 
fire, it is always best to make an opening through 
the coal to the grate-bars, so that the air from the 
bottom of the furnace can act directly on the wood 
and increase the combustion. 

Q. Should an engineer give great attention to 
the regulation of the draught in the furnace ? 

A. Yes; the regulation of draught is one of the 
most important of an engineer's duties; in fact, 
it is next in importance to the regulation of the 
water in the boiler. 

Q. How do you explain that ? 

A. Because it is well known that immense 
quantities of fuel are recklessly wasted by igno- 
rance and carelessness in the management of the 
draught. 

Q. How should an engineer regulate his draught 
to obtain the best results from the fuel ? 

A. He should have no more draught at any time 
than would produce a sufficient combustion of the 



STEAM ENGINEERS AND ELECTRICIANS. 115 

fuel to keep the steam at the working pressure, as 
by opening the clamper to its utmost limits great 
quantities of heat are carried into the chimney 
and lost. 

Q. Can an engineer carry out this principle of 
regulating the draught in all cases ? 

A, No; only in furnaces and boilers that are 
sufficiently large to furnish the necessary amount 
of steam without forcing. Of course, where the 
boiler is too small for the engine, or has not suf- 
ficient heating surface it is impossible to economize 
fuel. 

Q. Is it objectionable to throw steam or water 
under the grate-bars of locomotive boilers, when 
such boilers are used for stationary engines ? 

A. Yes; as steam or water in the ashpit forms 
a lye with the ashes and corrodes the iron and 
destroys the water-legs of the boiler. 

Q. Should an engineer in all cases keep his ash- 
pit clean ? 

A. Yes; by allowing the ashpit to become filled 
with ashes and cinders the air becomes heated to 
a high temperature before entering the fire; the 
grate-bars also become overheated, and in many 
cases either badly warped or melted down. 

Q. How should an engineer keep his safety 
valve ? 

A. He should keep it at all times in good work- 



116 roper's catechism for 

ing order, and move it at least once a day, partic- 
ularly in the morning, 

Q. AVhy should he move the safety-valve every 
morning ? 

A. To see that all its parts are in good working 
order before getting up steam. 

Q. Would you consider it reprehensible conduct 
on the part of an engineer who would weight his 
safety-valve in order to carry a pressure greater 
than that he knew to be safe ? 

A. Yes; such conduct, if proved, ought to be 
sufficient to disqualify any engineer from ever 
taking charge of an engine and boiler again. 

Q. What is the duty of an engineer in regard to 
blowing out his boilers ? 

A. He should carefully remove all the fire from 
the furnace, and see that the steam is at the proper 
pressure, say from 45 to 50 pounds. He should 
also close his damper. 

Q. Should any time intervene between the 
drawing of the fire and the blowing out of the 
boiler? 

A. Yes; at least one hour. 

Q. Why should the blowing out of the boiler 
be deferred for an hour after the fire is drawn ? 

A. To allow the furnace to cool, and prevent 
the boiler from being injured with the heat after 
the water is all blown out. 



STEAM ENGINEERS AND ELECTRICIANS. 117 

Q. Why not blow out the boiler under a high 
pressure of steam, say 70, 80, or even 90 pounds 
to the square inch ? 

A. Because the higher the steam pressure the 
higher the temperature of the iron, so that by 
blowing out the boiler under a high steam pressure, 
the change is so sudden that it has a tendency to 
contract the iron and cause the boiler to leak. 

Q. Should the engineer fill his boiler with cold 
water immediately after blowing out ? 

A. No; as the introduction of cold water into 
the boiler before the temperature of the iron 
becomes lower would in all probability cause the 
boiler to leak. 

,Q. How often should an engineer blow out his 
boiler ? 

A. Whenever he discovers any appearance of 
mud in the water. 

Q. Is it not customary with some engineers and 
owners of steam boilers to blow^ out their boilers 
once a week ? 

A. Yes; but the wisdom of this practice is 
doubtful. When fresh water is boiled, it is sup- 
posed to deposit its minerals, and after that it is 
not advisable to blow out the pure water and fill 
the boiler with water holding matter in solution 
and suspension. How often a boiler should be 
blown out depends on the nature of the water used. 



118 roper's catechism for 

Q. Should an engineer, when filUng his boilers, 
open some cock or valve in the steam room of the 
boiler and allow the air to escape ? 

A. Yes; otherwise the air would retard the 
ingress of the water, and also collect in the steam 
room of the boiler and prevent the regular expan- 
sion of the iron when the fire is started. 

Q. What do you mean by the steam room of a 
boiler? 

A. 1 mean that portion of the boiler occupied 
by steam above the water. 

Q. AVhat is meant by the water room in a steam 
boiler ? 

A. That portion of the boiler occupied by water. 

Q. What do you call the fire-line of the boiler ? 

A. The fire-line of the boiler is a longitudinal 
line above which the fire cannot rise on account of 
the masonry by which the boiler is surrounded. 
• Q. How often should an engineer clean the tubes 
or flues of his boiler ? 

A. At least once a week; he should also remove 
all ashes and soot that become attached to the out- 
side of the boiler. 

Q. What advantage is gained by cleaning the 
flues and tubes regularly, and also removing the 
soot and ashes that become attached to the boiler ? 

A. It makes a great saving in fuel, as it allows 
the fire to act directly upon the iron. 



STEAM ENGINEERS AND ELECTRICIANS. 119 

Q. How often should an engineer clean his 
boilers ? 

A. Every three months, if possible. 

Q. Should an engineer, when cleaning his boil- 
ers, examine all stays, braces, seams, and angles 
of the boiler or boilers ? 

A. Yes; he should make a thorough examina- 
tion of all parts of the boiler, seams, rivets, 
crown-sheet, crown-bars, crow-feet, cotters, and 
braces; he should also sound the shell of the 
boiler with a very light steel hammer. 

Q, Why should the engineer sound the boiler? 

A. Because it is the only way in which he can 
determine the condition of the iron. 

Q. How often should an engineer test his steam- 
er pressure-gauge ? 

A. At least once a year. 

Q. Can an engineer test a steam-gauge himself ? 

A. No; unless he has a test-gauge, which is not 
very often the case. The gauge ought to be tested 
by another gauge built or made expressly for that 
purpose. 

Q. How should an engineer keep his glass 
water-gauges ? 

A. He should keep them perfectly clean inside 
and out. 

Q. How can an engineer clean his glass water- 
gaus'es inside ? 



120 roper's catechism for 

A. By opening the drip-cock and closing the 
water- valve, and allowing the steam to rush down 
the glass and carry out the mud or sediment. 
They should also be swabbed out with a piece of 
' cloth or waste on a small stick, when the boiler is 
cold; but care should be taken not to touch the 
inside of the glass with wire or iron, as an abrasion 
Avill immediately take place. 

Q. In case an engineer has a glass water-gauge, 
should he neglect his gauge-cocks ? 

A. No; he should examine them several times 
in the day, see that they are in good working order, 
and grind or repair them if necessary. He should 
always be sure to shut them tight, as by leaving 
them loose the steam and water destroy the seat 
of the valve and render them useless. 

Q. What evidence do dirty or broken glass 
gauges, filthy boiler-heads, leaking and muddy 
gauge-cocks give of a man's ability as an en- 
gineer ? 

A. They furnish strong evidence of his igno- 
rance or neglect of duty. 

Q. What should an engineer do in cold weather, 
when his pumps, boiler connections, steam gauges, 
or water-pipes are liable to be frozen ? 

A. He should open all drip- or discharge-cocks 
and allow the water to run out when he stops work 
at night, and in the morning make a thorough 



STEAM ENGINEERS AND ELECTRICIANS. 121 

examination of all steam- and water-connections 
before he starts his fires. 

Q. In case it becomes necessary to stop the 
engine, and the steam commences to blow off at 
the safety-valve, what is the duty of the engineer ? 

A. He should immediately start his pump or 
injector, and also cover his fire with fresh coal, so 
that the circulation might be kept up by the feed- 
water, and the extreme heat of the fire absorbed 
by the fresh coal, instead of being communicated 
to the iron of the boiler; and he should not 
attempt, under any circumstances, to interfere 
with the free escape of the steam through the 
safety-valve. 

Q. Whenever the fire-door of the furnace is 
open, should the damper be closed, if possible ? 

A. Yes; the door and the damper should never 
be open at the same time, unless it is absolutely 
necessary, as the cold air, that would otherwise 
have to pass through the fire and become heated, 
rushes in through the open door above the fire and 
impinges on the tube and crown-sheets, and has a 
tendency to contract the seams and cause leakage. 

Q. In case it should become necessary to ex- 
amine the check-valve while steam is on the boiler, 
how should it be done ? 

A. The stop-cock between the check-valve and 
boiler should be first closed before any attempt is 



122 roper's catechism for 

made to unscrew or remove the check. Any 
neglect to close the stop-cock might result in a 
serious accident. 

Q. How should an engineer proceed to make a 
joint on the man-hole or hand-holes of his boiler ? 

A. He should first carefully remove all gum or 
other material from the seat or flange where the 
joint is to be made, so that the gasket may have a 
smooth and solid bearing before he commences to 
tighten the nut. 

Q. Do you know any other important duty an 
engineer should consider himself bound to per- 
form ? 

A. Yes; he should daily make a thorough ex- 
amination of all safety-valves, pumps, injectors, 
and all steam- and water-connections. 

Q. What should be said of an engineer who 
would allow his boiler and engine to run jon from 
bad to worse, expecting some day to have a general 
overhauling, instead of making repairs as they 
were needed ? 

A. He should be considered totally unfit for 
the position of an engineer. 

Q. When can it be said that an engineer has 
done his duty ? 

A. When he shows by his work that he has 
cared for everything connected with his engine and 
boiler in the best possible manner. 



STEAM ENGINEERS AND ELECTRICIANS. 123 



SCALE-FORMATION, CORROSION, FOAMING, 
AND PRIMING. 

Q. What are the results of scale in boilers, and 
why? 

A. Increased coal consumption and burning of 
the plates. Because the scale being a poor con- 
ductor of heat, the heat of the fire is not imparted 
to the water as completely as if the scale were not 
there. For the same reason the water does not 
protect the iron against crystallization and burning. 

Q. What, roughly, is the conductivity of scale 
as compared to iron ? 

A. About 1 : 35. 

Q. What are the principal ingredients contained 
in water which cause the formation of scale ? 

A. Sulphate of lime, phosphate of lime, car- 
bonate of lime, magnesia, silica, and alumina. 
In sea-water the most important of these is sul- 
phate of lime. 

Q. How may the formation of scale be checked ? 

A. By the use of boiler compounds. 

Q. Is there any boiler compound which will be 
effective in all cases ? 

A. No; the composition of a boiler compound 
should be determined by the nature of the im- 
purities. Thus, a proper amount of carbonate of 
soda introduced regularly with the feed- water 



124 roper's catechism for 

would prevent the formation of scale if the in- 
gredient in the water which tends to produce it is 
sulphate of lime; but this would be of no value 
if the scale - producing substance is silica or 
alumina. 

Q. What are 'the principal substances used to 
check the formation of scale ? 

A. Carbonate of soda if the scale-forming in- 
gredient is sulphate of lime; phosphate of sodium 
for the sulphates of lime and magnesium; milk 
of lime for the carbonates of lime and magnesium; 
caustic soda and soda ash for the carbonate and 
sulphate of calcium; and sulphate of magnesium 
and tannate of soda foT the sulphate and carbonate 
of lime. 

Q. How, then, should we proceed if it is found 
that an undue amount of scale forms in the 
boiler ? 

A. We should have a chemical analysis of the 
feed-water made and add sufficient quantities of 
the proper kinds of salts to transform the scale- 
producing ingredients into soluble salts. 

Q. In what other ways may the formation of 
scale be prevented ? 

A. The use of feed-w^ater heaters and purifiers 
of the open type is often sufficient, especially 
where the amount of impurity is not very great. 

Q. In what way does this remedy the difficulty? 



STEAM ENGINEERS AND ELECTRICIANS. 125 

A. By causing the impurities to be deposited 
in the heater or purifier, where they can do no 
harm and whence they may easily be removed 
without interfering with the operation of the plant. 

Q. What is meant by corrosion ? 

A. By corrosion is meant the wasting, pitting, 
or grooving of the iron in the boiler. 

Q. To what is it generally due ? 

A. External corrosion is due to the chemical 
action of sulphur or other products contained in 
the fuel and in the atmosphere. Internal corro- 
sion is caused by the chemical action of acid and 
mineral substances contained in the water. 

Q. AVhat are the remedies ? 

A. Numerous remedies are employed to prevent 
internal corrosion, such as painting the interior of 
the boiler with Portland cement, allowing a thin 
layer of scale to form, or suspending metallic zinc 
in the water and steam spaces, all of which are 
effective in some cases. There seems to be no 
effectual remedy against external corrosion when 
produced by foreign substances contained in the 
fuel. 

Q. What is meant by foaming ? 

A. By foaming is meant a violent agitation of 
the water in the boiler. It can be detected by the 
rising and falling of the level of the water in the 
gauge glass and by its disturbed condition. 



126 roper's catechism for 

Q. What is the cause of foaming in steam 
boilers ? 

A. Foaming in steam boilers might be attributed 
to different causes. First^ to the boiler not having 
a sufficient amount of steam-room, so that when- 
ever the valve opens to admit steam to the cylinder, 
the pressure on the surface of the water is less- 
ened, allowing the water to rise up from the bot- 
tom of the boiler. Second^ foaming is sometimes 
caused by the foul condition of the boiler; but in 
such cases it will be easy to discover the cause, as 
the water in the glass gauge will appear quite 
muddy. Third, foaming is caused by the presence 
of any substance of a soapy or greasy nature in 
the water. But whatever may be the cause of 
foaming, it is always attended with great danger 
to the boiler and a certain amount of injury to the 
engine. 

In all cases where a boiler foams badly, the 
water is lifted from the fire-surface of the boiler, 
and allows the iron to burn; also, the mud and 
water from the boiler are carried over with the 
steam to the cylinder, occupying the clearance 
between the piston and the head of the cylinder, 
not only destroying the surface of the cylinder by 
the grit and dirt, but in many cases causing the 
fracture of the cylinder-head. 

Q. What is the best preventive against foaming ? 



STEAM ENGINEERS AND ELECTRICIANS. 127 

A. The best preventives against foaming are — 
First, a clean boiler. Second, pure water. Third, 
a sufficient amount of steam-room. Fourth, a 
steam pipe well proportioned to the size of the 
engine. 

Q. What is meant by priming ? 

A. The passage of water from the boiler to the 
cylinder of the engine in the shape of spray. 

Q. How may it be detected ? 

A. By the appearance of the exhaust from the 
engine, which, when moist, is white instead of 
colorless, as is the case when dry, and by a click- 
ing noise in the cylinder, which almost invariably 
accompanies the presence of moisture. 

Q. AVhat causes priming ? 

A. Usually the want of sufficient steam space 
in the boiler, or the water being carried at too 
high a level. 



128 roper's catechism for 

ADJUNCTS OF STEAM BOILERS. 

THE SAFETY-VALVE. 

The form and construction of this indispensable 
adjunct to the steam boiler are of the highest 
importance, not only for the preservation of life 
and property, which would in the absence of this 
means of safety be constantly jeopardized, but also 
to secure the durability of the steam boiler itself. 

Increasing the pressure to a dangerous degree 
would be impossible in any boiler if the safety- 
valve were what it is supposed to be, — a perfect 
means for liberating all the steam which a boiler 
may produce with the fires in full blast, and all 
other means for the escape of steam closed. Until 
such a safety-valve shall be devised and adopted 
in general use, safety from gradually increasing 
pressure must depend on the attention and watch- 
fulness of the engineer. 

Q. AVhat is the object of the safety-valve? 

A. It is a valve intended to relieve the boiler 
from extra pressure, and prevent bursting, col- 
lapse, or explosion. 

Q. How is this accomplished ? 

A. By balancing the steam pressure against that 
of a spring or weight in such a way that when the 
pressure in the boiler exceeds the limit of safety, 



STEAM ENGINEERS AND ELECTRICIANS. 129 

it overcomes the action of the spring or weight 
and opens a valve, allowing the surplus pressure 
to be relieved. 

Q. How often should the safety-valve be moved ? 

A. At least once a day, more particularly in the 
morning. 

Q. Why should the safety-valve be moved in 
the morning? 

A. So as to be sure that it is in good working 
order before starting the fire. 

Q. What are the most important principles to be 
adhered to in the construction of the safety-valve ? 

A. Simplicity of construction, directness, and 
freedom of action. 

Q. Does the safety-valve become worn and 
leaky by the continual action of the steam ? 

A. Yes; all safety-valves become leaky and 
ought to be ground carefully on their seats. 

Q. What is the best material to use for grinding 
safety-valves ? 

A. Pulverized glass, grit of grinding-stones, or 
fine emery. 

Q. Should safety-valves be constructed with 
loose or vibratory stems ? 

A. Yes; as the rigid or solid stem is apt to be- 
come jammed by the canting of the lever and 
weight, and in such cases the higher the pressure 
the more difficult it is for the valve to open. 



130 roper's catechism for 

Q. What are the principal kinds of safety- 
valves ? 

A. There are three principal classes, namely: 

(a) The dead-weight safety-valve, in which 

the pressure of the steam is balanced 
by a weight placed directly on the 
valve-spindle. 

(b) The spring safety-valve, which is similar 

to the above except that the weight 
is replaced by a spring. 

(c) The lever safety-valve, in which a weight 

or spring, instead of acting directly 
on the valve-spindle, is attached at 
the end of the lever, the adjustments 
being made by altering its position 
on the lever. 
Q. What are the relative advantages of springs, 
as compared to weights in safety-valves ? 

A. Weights have the advantage that they do 
not change, which springs are liable to do when 
in tension. On the other hand, weights could not 
be used on vessels or locomotives on account of 
the motion; the momentum which the weight 
would acquire would constantly alter the blowing- 
off pressure. For these reasons weight safety- 
valves are mostly used in connection with station- 
ary boilers, while spring safety-valves are used 
exclusively for marine and locomotive boilers. 



STEAM ENGINEERS AND ELECTRICIANS. 131 

Q. How are safety-valves set for a given blowing- 
oif pressure in the dead- weight and spring type ? 

A. By simply adjusting the weight or the ten- 
sion of the spring until it is equal to the blowing- 
off pressure in pounds per square inch, times the 
area of the valve in square inches. 

Q. How do you calculate what weight should 
be placed on the end of a given lever safety-valve 
for a certain blowing-off pressure? 

A. Multiply the area of the valve in square 
inches by the blowing-off pressure in pounds per 
square inch and the distance of the valve from 
the fulcrum in inches; multiply the weight of the 
lever in pounds by the distance of its center of 
gravity from the fulcrum in inches; multiply the 
weight of the valve and steam in pounds by their 
distance from the fulcrum in inches; add the last 
two products together, subtract their sum from 
the first product and divide the remainder by the 
total length of the lever. The quotient will be 
the required weight in pounds. 

Q. How do you calculate the distance of the 
weight from the fulcrum for a given blowing-off 



pressure 



? 



A. Multiply the pressure by the area and the 
distance from the fulcrum from the valve; multi- 
ply the weight of the lever by the distance of its 
center of gravity from the fulcrum; multiply the 



132 



roper's catechism for 



weight of the valve and stem by their distance 
from the fulcrum; add the last two products, 
deduct them from the first product, and divide 
the remainder by the weight of the ball. The 
quantities being again taken in pounds and inches, 
the result will be the distance of the weight from 
the fulcrum in inches. 

Q. How do you calculate the bloAving-off pres- 
sure for a given position of the ball ? 




A. Multiply the weight of the valve and stem 
in pounds by their distance from the fulcrum. 
Multiply the weight of the lever by the distance 
of its center of gravity from the fulcrum. Multi- 
ply the weight of the ball by its distance from the 
fulcrum. Multiply the area of the valve by its 
distance from the fulcrum. Divide the sum of 
the first three products by the last product. The 



STEAM ENGINEERS AND ELECTRICIANS. 133 

quantities being all taken in pounds and inches, 
the result will be the pressure at which the valve 
will blow off in pounds per square inch. 

Q. How can these three rules be expressed by 
simple formulse ? 

A. If in the diagram on opposite page — 
W = weight of ball in pounds, 
w = weight of valve and stem in pounds, 
ii\ = weight of lever in pounds, 
l^ = distance from fulcrum to valve in 

inches, 
Zj = distance from valve to ball in inches, 
I = distance from fulcrum to center of 

gravity of lever in inches, 
p z= steam pressure in pounds per square 

inch, 
a = area of valve in square inches, — 
then : 

pal, = 10 l^ + u\ I + W (/, -f g 
_ p a /, — [w I, + IV, q 

^ ~ a I, 

pal, — IV I, — IV, I 

Q. How would you find the distance of the 
center of gravity of a lever from the fulcrum ? 



134 ropee's catechism for 

A. If the lever is of "aniform cross-section, as in 
the diagram shown on page 132, the center of 
gravity would be at its middle point; but if the 
lever is taper, proceed according to the following — 
Rule for finding the distance of the center of 
gravity of taper levers from the fulcrum. — To the 
width of the small end of the lever add one-third 
of the difference, in width, between the large and 
the small end of the lever. Multiply the sum by 
the length of the lever, and divide the product by 
the sum of the large and the small end of the 
lever, all in inches. The quotient will be the re- 
quired distance in inches. 

Q. How would you express this in a formula ? 
A. If we let — 

a = width of the large end in inches, 
b = width of the small end in inches, 
I = distance of center of gravity from 

fulcrum in inches, 
L = total length of lever in inches, — 
the formula is: 

_ g 4- 2 5 L 
~ a + 6 • 3 * 

Q. With the aid of this rule and the one given 
on page 133, find the weight to be placed at the 
end of the lever of a safety-valve under the fol- 
lowing conditions : 



STEAM ENGINEERS AND ELECTRICIANS. 135 

width of large end of lever = 3 inches, 

width of small end of lever = 2 inches, 

total length of lever = 30 inches, 

area of valve = 7 sq. inches, 

weight of lever = 9 pounds, 

weight of valve and stem - = 6 inches, 

distance of valve stem from 

fulcrum = 3 inches, 

blowing-off pressure = 60 pounds. 

A. By the rule for finding the distance of center 

of gravity, we have 

, 3 + 2x2^ 30 ,,.. 
I = — g I 2 — X -Q- = 14 mches. 

By the rule for finding the weight of the ball, 
we have 

60 X 7 X 3 — [6 X 3 + 9 X 14] 
^~ 30 

= 37.2 pounds 
for the required weight to be placed at the end of 
the lever. 

Q. Suppose this weight were moved back so 
that its distance from the fulcrum became 26 
inches, at what pressure would the valve blow off ? 
A. By the second formula, 

6X3 + 9X14 + 37.2 X 26 ^„ , 

p =rz 1 x Z ^ pounds. 

Q. Where should- the weight be placed, so that 
the valve would blow off at a pressure of 45 pounds ? 



136 roper's catechism for 

A. By the third formula, 

45X7X3 — 6X3 — 9X14 
^i-f^2— 37 2 

= 21^ inches from fulcrum. 

Q. How large should the area of safety-valves 
be made for different sizes of boilers ? 

A. There are a great many rules governing the 
areas of safety-valves. Some rules base it on the 
heating surface, some on the grate surface, some 
on the coal consumption, some on the water 
evaporated, and some on the heating surface and 
gauge pressure. The rule given by Professor 
Thurston gives average values. It is as follows: 

Rule. Multiply the heating surface in sq. feet 
by 5 and divide the product by 10 plus the gauge 
pressure in pounds per sq, inch. The quotient 
divided by 2 gives the proper area in square inches. 

Q. How much steam should a safety-valve be 
capable of discharging? 

A. About twice as much as that corresponding 
to the rated capacity of the boiler, because when 
the boiler is forced to the utmost it is capable of 
generating a much greater quantity of steam than 
its rating calls for. 

Q. Should a boiler have only one safety-valve? 

A. No; it should have at least two, for each 
boiler fired separately or for each set of boilers 
placed over one fire. 



STEAM ENGINEERS AND ELECTRICIANS. 



137 



A TABLE FOE SAFETY-VALVES. 

Containing the Cikcumfeeences and Aeeas of 

Circles from ^-^ of an inch to 4 inches. 



Diameter. 


Circumfer- 
euce. 


Area. 


Diameter. 


Circiinifei- 
euce. 


Area. 


tV 


.1963 


.0030 


2 ins. 


6.2832 


3.1416 


i 


.3927 


.0122 


tV 


6.4795 


3.3411 


A 


.5890 


.0276 


i 


6.6759 


3.5465 


i 


.7854 


.0490 


A 


6.8722 


3.7582 


A 


.9817 


.0767 


i 


7.0686 


3.9760 


f 


1.1781 


.1104 


T% 


7.2649 


4.2001 


t\ 


1.3744 


.1503 


1 


7.4613 


4.4302 


^ 


1.5708 


.1963 


/f 


7.6576 


4.6664 


t\ 


1.7671 


.2485 


1 


7.8540 


4.9087 


1 


1.9635 


.3068 


fe 


8.0503 


5.1573 


H 


2.1598 


.3712 




8.2467 


5.4119 


f 


2.3562 


.4417 


H 


8.4430 


5.6727 


f 


2.5525 


.5185 


1 


8.6394 


5.9395 


2.7489 


.6013 


if 


8.8357 


6.2126 


if 


2.9452 


.6903 


i 


9.0321 


6.4918 








11 


9.2284 


6.7772 


lin. 


3.1416 


.7854 








t 


3.3379 


.8861 


3 ms. 


9.4248 


7.0686 


3.5343 


.9940 


tV 


9.6211 


7.3662 


tV 


3.7306 


1.1075 


? 


9.8175 


7.6699 


•i 


3.9270 


1.2271 


A 


10.0138 


7.9798 


tV 


4.1233 


1.3529 


I 


10.2102 


8.2957 


1 


4.3197 


1.4848 


T% 


10.4065 


8.6179 


tV 


4.5160 


1.6229 


f 


10.6029 


8.9462 


^ 


4.7124 


1.7671 


tV 


10.7992 


9.2806 


A 


4.9087 


1.9175 


i 


10.9956 


9.6211 


1 


5.1051 


2.0739 


A 


11.1919 


9.9678 


H 


5.3015 


2.2365 


1 


11.3883 


10.3206 


f 


5.4978 


2.4052 


il 


11.5846- 


10.6796 


f 


5.6941 


2.5801 


i 


11.7810 


11.0446 


5.8905 


2.7611 


f 


11.9773 


11.4159 


H 


6.0868 


2.9483 


12.1737 


11.7932 








if 


12.3700 


12.1768 








4 ins. 


12^.5664 


12.5654 



138 roper's catechism for 

GAUGES. 

Q. What is meant by a gauge ? 

A, A gauge is any instrument or device used 
for measuring. 

Q. What are the princijDal gauges used in con- 
nection with steam boilers ? 

A, The steam pressure gauge, vacuum gauge^ 
water gauge, sahnometer, and econometer. 

Q. Describe the steam gauge. 

A. There are two kinds: those which merely 
indicate the pressure and those which make a 
permanent record of it. Both are usually con- 
structed on the principle invented by Bourdon, 
and consist of a thin tube of elliptical cross-sec- 
tion, bent into a curved shape. The steam whose 
pressure is to be measured is admitted into the 
tube and tends to make the cross-section circular. 
This tendency causes the tube to straighten itself 
out partially, and the instrument is so constructed 
with a pointer and gearing that the straightening 
of the tube moves the pointer which indicates the 
pressure within on a suitable dial. The recording 
gauge has, in addition, a clock which moves the 
dial, giving it one revolution in 24 hours, so that 
by the aid of a pen or stylus filled with ink a 
complete record of the pressure carried during this 
time can be had. 



STEAM ENGINEERS AND ELECTRICIANS. 139 

Q. Do steam gauges register absolute pressure ? 

A. No; they are usually constructed to indicate 
pressure above the atmosphere — that is, at atmos- 
pheric pressure (14.7 pounds per square inch) the 
pointer stands at zero. 

Q. What precautions should be taken in using 
pressure gauges ? 

A. The pointer should always stand at zero 
when there is no pressure in the boiler. If it 
does not, it should be adjusted. Even after this 
is done, the readings at other pressures may be 
incorrect and its readings should be checked from 
time to time by comparing with a standard gauge 
which is known to be correct. 

Q. What is a vacuum gauge ? 

A. It is made in the same way as a pressure 
gauge, but it is arranged to read pressures below 
the atmosphere instead of above. 

Q. How are vacuum gauges calibrated ? 

A. They are usually calibrated in inches of 
mercury instead of pounds, — that is to say, the 
readings indicate to how many inches the vacuum 
would allow a column of mercury to rise under 
atmospheric pressure. Each inch of mercury 
corresponds roughly to a vacuum of about half a 
pound, so that a reading of 20" on a vacuum 
gauge would mean that the pressure is about 10 
pounds below that of the atmosphere. 



140 roper's catechism for 

Q. Why are they calibrated in this way and not 
in absolute pressures ? 

A. Because the mechanism which operates the 
gauge depends for its action upon the difference in 
pressure of the atmosphere and vacuum chamber; 
hence, as the pressure of the atmosphere varies, 
the gauge would not be accurate if calibrated in 
pounds absolute pressure. 

Q. What is a water gauge ? 

A. It is a device for indicating the level of the 
water in the boiler. It usually consists of a plain 
glass tube placed on the outside of the boiler, and 
connected at the top to the steam- and at the bot- 
tom to the water-space. 

Q. What is a safety water column ? 

A. It is a modification of a glass water gauge, 
with floats so arranged that a signal is given both 
when the water is too high and when it is too low. 

Q. Do you consider the use of safety water 
columns advisable? 

A. The}^ are very useful where an engineer or 
fireman has other duties to perform besides attend-, 
ing to the boiler; but it is a mistake for engineers 
to neglect watching the water-level on account of 
this device becau-se it may get out of order. 
There can be nothing so dangerous in running 
boilers as neglecting the water. In some instances 
where these safety water columns were used, the 



STEAM ENGINEERS AND ELECTRICIANS. 141 

firemen have been known to systematically fall 
asleep and depend on the alarm in the safety water 
column to awaken them at the proper time. 

Q. Is the glass gauge the only device used for 
indicating the water-level ? 

A. No ; every boiler should, in addition, be 
fitted with gauge cocks placed at different levels. 
These are partly for the purpose of checking up 
the glass gauge and partly for use in case the 
gauge glass should break, which is not an infre- 
quent occurrence. 

Q. What is the salinometer ? 

A. It is an instrument or gauge used for indi- 
cating the quantity of salt contained in the water 
of marine boilers. 

Q. What is the econometer ? 

A. It is an instrument or gauge used for indi- 
cating, continuously and automatically, the quan- 
tity of carbonic acid contained in the products of 
combustion. 

Q. How much carbonic acid should they con- 
tain? 

A. As much as possible. 

Q. How can this be attained ? 

A. By supplying enough air to the furnace for 
a complete combustion of the fuel, but not much 
in excess of that amount. 

Q. What is the result if too much air is supplied ? 



142 



ROPER S CATECHISM FOR 



A. A portion of the heat of combustion is con- 
sumed in raising the temperature of the excess of 
air and consequently wasted. The following table 
shows the amount of wasted fuel for different per- 
centages of carbonic acid in the flue gases: 



TABLE 

SHOWING WASTE OF FUEL DUE TO EXCESSIVE SUPPLY 
OF AIR. 

(coal of medium quality.) 



Percentage carbonic acid 
in flue gases, 


2 


4 


6 


8 


10 


12 


14 


No. of times the quan- 
tity of air required for 
complete combustion, . 


9.5 


4.7 


3.2 


2.4 


1.9 


L6 


1.4 


Percentage waste of fuel 
at420OFahr., 


90 


45 


30 


23 


18 


15 


13 



PUMPS AND INJECTORS. 

Q. What is a pump ? 

A. It is a device for lifting, forcing, or transfer- 
ring water or other liquids. 

Q. How are pumps usually operated ? 
A. (a) By belting or gearing from some power 
shaft, called power pumps. 
(6) By the direct connection to a steam 
cylinder equipped with suitable valve 



STEAM ENGINEERS AND ELECTRICIANS. 143 

gear for the distribution! of the steam, 
called steam pumps, 
(c) By direct connection or gearing to an 
electric motor ; these are called electric 
pumps. 
Q. Which of the above types is usually adopted 
for feeding boilers ? 
A. The steam pump. 

Q. What different kinds of steam pumps are 
there ? 

A. (a) Fly-wheel pumps — those in which the re- 
ciprocating motion of the steam piston 
is first converted into rotary motion 
by means of a crank shaft, with a fly- 
wheel to help it over the dead cen- 
ters, and then re-converted by another 
crank and rods into reciprocating mo- 
tion for the water cylinder. 
(6) Direct-acting pumps — those in which the 
water piston or plunger is mounted- 
on the same rod as the steam piston 
and the power transmitted from the 
latter to the former, direct and with- 
out the intervention of a crank shaft 
and fly-wheel. In this type an auxil- 
iary valve gear is required in addition 
to the main valve gear, to help the 
machine over its dead points. 



144 roper's catechism for 

(c) Duplex pumps — consisting of a combina- 
tion of two pumps so coupled together 
that the steam-valve of the one is 
operated by the piston of the other, 
and vice versa. 

Q. Which of these is most commonly used as a 
boiler-feed pump ? Why ? 

A. The duplex pump, because it is the simplest. 

Q. W^hat is the difference between a force pump 
and a suction pump ? 

A. A force pump is one in which the energy is 
expended in forcing the water against some oppos- 
ing pressure, such as that in the boiler. A suction 
pump is one which takes the water from a lower 
level than that of the pump, as, for example, a 
pump placed at the top of a well. 

Q. Is there any limit beyond which water can-, 
not be lifted by a suction pump ? Give reasons. 

A. Yes; water cannot be lifted by a suction 
pump over 33 feet vertically, and it will deliver 
water slowly only, at this height. The reason for 
this is that the pump does not actually lift the 
water, but merely creates a vacuum in the water 
cylinder, and the water is lifted by the atmospheric 
pressure on its surface. The atmospheric pressure 
will support a column of water about 33 feet in 
height, hence this is the limit beyond which water 
cannot be raised by a suction pump. If the pump 



STEAM ENGINEERS AND ELECTRICIANS. 145 

and the piping is tight, however, it will draw 
water horizontally almost any distance. 

Q. Is there any limit in the height to which a 
piimp will force water ? 

A. None; except the power of the pump. 

Q. How do you calculate the power required to 
pump water ? 

A. Multiply the number of pounds of water to 
be pumped per minute by the vertical distance, in 
feet, between the levels of the supply and dis- 
charge, and divide the product by 33,000; the 
result will be the theoretical horse-power. To 
this must be added the losses in friction corre- 
sponding to the velocity of the water (see page 63). 
If instead of pumping the w^ater to a higher level 
it is required to force it against a pressure, multi- 
ply by 2J times the pressure instead of the 
height, making the same correction for losses as 
above. 

Q. How do 3^ou determine the capacity of boiler- 
feed pumps ? 

A. Calculate the amount of water which the 
boiler is capable of evaporating under normal 
conditions by multiplying the horse-power of the 
boiler by 30. This will give the number of pounds 
of water it will evaporate per hour. Divide this 
by 8.35, which will give the number of gallons. 
The pump should be capable of supplying about 
10 



146 roper's catechism for 

double this quantity, so that it will be adequate 
when the boiler is forced. 

Q. When the water is hot, what precautions 
must be taken with the pump ? 

A. It should be brass-lined so that it will not 
corrode, and it must be placed below the level of 
the water-supply, as otherwise the hot water will 
not follow the plunger. It is also advisable to 
place a valve between the supply and the pump, 
so that any accumulated vapor may be liberated. 

Q. What is an injector? 

A. It is an apparatus for forcing water against 
a pressure by the direct action of a jet of steam 
upon a mass of water. 

Q. Briefly describe the injector and its action. 

A. It consists of a steam nozzle through which 
enters the steam used ; a water-supply tube 
through which enters the water to be forced ; a 
combining tube which begins at the end of the 
steam nozzle, being that part of the apparatus 
where the steam and water first come in contact; 
and, finally, a delivery tube from which the mix- 
ture of steam and water enters the discharge pipe. 
All of these parts have peculiar shapes, which 
have been determined by years of experimenting; 
the object being to give the steam and water the 
proper velocities at different stages in the process. 
The action of the apparatus may be explained as 



1 



STEAM ENGINEERS AND ELECTRICIANS. 147 




INJECTOR. 

S, Steam nozzle. 

B, Spinale for adjusting supply of 

C, Combining tube. 
Z>, Delivery tube. 



148 roper's catechism for 

follows : The steam leaves the nozzle and enters 
the combining tube at a high velocity. The 
friction between the steam jet and the air in the 
water-supply pipe causes the latter to be exhausted 
and consequently the water being relieved of the 
pressure upon its surface soon rises and enters the 
combining tube, where it comes in contact with 
the steam jet and condenses it. In being con- 
densed the cross-section of the steam jet is greatly 
reduced, and the entire energy of its velocity is 
concentrated upon a very thin jet. This energy 
being more than sufficient to force it into the 
boiler, some of it is imparted to the water which 
it meets in the combining tube, and the entire 
mixture of steam and water is carried into the 
delivery tube and thence into the boiler by virtue 
of the momentum which it has acquired. Of 
course, the apparatus must be carefully propor- 
tioned, since if there is too much water the 
energy of the condensed steam will not be suf- 
ficient to carry it into the boiler, while if there 
is too little, the steam will not be condensed. 

Q. What are the advantages of injectors over 
pumps ? 

A. The principal advantages are that water 
enters the boiler in a steady stream; practically 
none of the energy of the steam used to operate 
it is wasted, as all the energy in excess of that 



STEAM ENGINEERS AND ELECTRICIANS. 149 

necessary to force the water into the boiler is 
utilized in raising its temperature; the water does 
not enter the boiler cold — it is more compact and 
has no moving parts. 

Q. What is the commonest cause of the failure 
of injectors to operate ? 

A. The presence of air in the suction pipe. 
This must be avoided by properly packing the 
valve stem and by entirely submerging the end of 
the suction pipe. Sediment or dirt in the nozzles 
will also interfere with the proper working of the 
apparatus. They should be carefully cleaned out 
if this occurs. 

Q. If the injector does not get water, where 
would you look for the trouble ? 

A. It would probably be due to one of the fol- 
lowing causes: a leak in the supply pipe, clogging 
up of the strainer, too hot water, too low a steam 
pressure for the required lift, or the water-supply 
may be cut off. I should examine the water pipe 
first to see that it was intact. 

Q. If the injector starts, but afterward the jet 
breaks, where would you expect to find the 
difficulty ? 

A. Any of the causes given in the preceding 
answer might produce this result, or the trouble 
might be caused by a loose disc in the valve in the 
supply pipe, causing it to partly close. In the 



150 roper's catechism for 

■ latter case, the trouble could be remedied by- 
reversing the valve. 

Q. What is the difference between lifting and 
non-lifting injectors? 

A. In the former there is a partial vacuum 
formed in the feed pipe on starting, in the latter 
a pressure is required in the water-supply. 

Q. What are the principal points to be observed 
in setting up injectors ? 

A. All pipes, whether steam, water-supply, or 
delivery, must be of the same or greater internal 
diameter than the hole in the corresponding branch 
of each injector, and as short and straight as 
practicable. When floating particles of wood or 
other matter are liable to be in the supply water, 
a strainer must be placed over the receiving end of 
the water-supply pipe. The holes in this strainer 
must be as small as the smallest opening in the 
delivery tube, and the total area of all the holes 
must be much greater than the area of the water- 
supply pipe, to compensate for the closing of some 
of them by deposits. The steam should be taken 
from the highest part of the boiler, to avoid the 
carrying over of water with the steam. ' ' Dry 
pipes ' ' should always be used on locomotives to 
insure dry steam; wet steam cuts and grooves the 
steam spindle and steam nozzle. The steam should 
not be taken from the steam pipe leading to an 



STEAM ENGINEERS AND ELECTRICIANS. 151 

engine, unless such pipe is large. Sudden varia- 
tions in pressure may break the jet. After all the 
pipes are properly connected to the injector and to 
the boiler, and before steam and water are admitted 
through them to the injector, they should be dis- 
connected and well washed out by blowing steam 
or running water through them, to wash out all 
red lead, scale, or other solids that may be in the 
pipes. Finally, in setting injectors it is important 
to place them as low as possible, since their 
capacity is reduced and the promptness and relia- 
bility of their action diminished as the height of 
lift is increased. 

Q. What is an inspirator ? 

A. It is a double-jet injector — that is, one con- 
taining two sets of jets, of which one is used for 
lifting the water from the source of supply and 
the other for forcing it into the boiler. 

Q. What is an ejector? 

A. It is an instrument similar to the injector, 
but designed for lifting water only, without forcing 
it against a pressure. 

Q, Is an injector more economical than a pump 
as a boiler feeder ? 

A. Not always; the injector is the more eco- 
nomical of the two when the feed-water is cold, 
but the pump is the more economical when the 
feed-water has been heated. 



152 



ROPER'S CATECHISM FOR 



TABLE* 

SHOWING THE EELATIVE EFFICIENCIES OF PUMPS 
AND INJECTORS. 



Method of Supplying Feed- 
Water TO Boiler. 

Temperature of feed-water as deliT- 
ered to the pump or to the injector, 
60° Fahr. Rate of evaporation of 
boiler, lOpounds of water per pound 
of coal from and at 212° Fahr. 


Relative amount 
•of coal required 
per unit of time, 
the amount for a 
direct-acting 
pump, feeding 
water at 60°, with- 
out a heater, being 
taken as unity. 


Saving of fuel 
over the amount 
required when 
the boiler is fed 
by a direct- 
acting pump 
without heater. 


Direct-acting pump, feeding 
water at 60°, without a 






heater, 


1.000 
.985 


.0 


Injector feeding water at 150°, 
without a heater, .... 


1.5 per ct. 


Injector feeding through a 
heater in which the water 






is heated from 150 to 200°, 


.938 


6.2 " 


Direct-acting pump feeding 
water through a heater, in 
which it is heated from 60 






to 200°, 


.879 


12.1 *• 


Geared pump, ran from the 




engine, feeding water 
through a heater, in which 
it is heated from 60 to 200°, 


.868 


13.2 *' 



* Computed by Professor D. S. Jacobus. 



STEAM ENGINEERS AND ELECTRICIANS. 153 

Q. Should a boiler plant have both a pump and 
an injector? 

A. Yes, whenever possible; because either the 
one or the other may at some time refuse to 
operate. In some cases it would be better to have 
two pumps, and in others two injectors. (See 
table on opposite page. ) 

Q. With what kind of boilers are injectors used 
the most ? Why ? 

A. AVith locomotives, because they use cold 
water, and therefore an injector is more efficient; 
also because the jarring motion of the engine does 
not affect an injector in the least, while its effect 
on the pump would be detrimental. An injector 
is also much lighter than a pump. 

HEATING FEED-WATER. 

Q. Why should the feed-water be heated before 
it enters the boiler? 

A. Because cold water fed into a boiler under 
steam produces strains that will shorten the life of 
the boiler; because a large proportion of the solid 
matter frequently contained in water will separate 
out at a high temperature, and, consequently, if , 
the feed-water is heated sufficiently solids will 
be deposited in the heater that would otherwise 
produce scale in the boiler; and because by using 
exhaust steam, or some other source of heat which 



154 



roper's catechism for 



0^ 




<r> 






^, 
















ro 
















o 


-* 


OS 




00 


c^ 


t^ 




M 


s 


§5 


?5 


^ 


s 


S 


^ 


s 


^ 


^ 


§5 


§5 


a^ 


_^_ 




o 














^ 


n 




ni 


^ 


^ 






























c5 


Oi 


s 


s 


';; 


^ 


S 


to 


J2 


Ui 


Tf 


^ 


CO 


CO 


2 


o 


s 


Tt< 


§ 


s 


^ 


g 


§ 


^ 


s 


^ 


S 


« 


s 


§8 


^ 


^ 


^ 


|0 


^ 


T}< 


cc 


CO 


^ 


^ 


^ 


S2 


^; 


;: 


S 


% 


lO 


rh 




in 


fn 


<-> 


r-1 


-f 


in 


j^ 


rf) 


ro 


m 


CO 


OS 












t- 










t- 








^ 


^ 


^ 


J2 


2 


s 


^ 


s 


c^ 


S 


^ 


O 


s 


a> 




OS 


m 


«o 


tn 


o 


„ 


^ 


IC 


o 


^ 


m 


nn 


^ 


^ 






























o 


s 


-* 


J2 




$^ 


^ 


^ 


;: 


;:: 


^ 


o 


o 


9i 


05 


OS 




Tl* 


^ 


05 


^ 


iro 


'^ 


'O 


^ 


f^ 


m 


rr, 


rr\ 


^ 


to 
















05 


lO 






























o 


o 


C5 


OS 


oi 


00 






'"' 


'"' 


'"' 


^ 


'"' 


'"' 


'"' 
















o 


OO 




r-1 


^ 


in 


f^ 






m 


m 


m 










o 








o 


to 








o 


to 




S2 






;: 


^: 


o 


s 


s 


CT. 


o> 






00 


'^ 


l> 




(M 


-^ 


to 


CO 


05 


o 


o 


o 


§ 


o 


05 


en 


t^ 


lO 






























t^ 








<^ 










ori 


on 


1^ 


J> 


to 


to 


'"' 


'-' 


^ 


" 
























o 








^ 


^ 








^ 


^ 








:| 


to 




















































lO 




'"' 


'"' 


'-' 


























Q 




-^1 




-1* 






^ 
















i2 


00 


"* 


o 








o 


to 


c^ 






05 


lO 


05 


S5 


05 






t^ 


t- 


t^ 










^ 




o 
















in 


m 


(M 










§ 


o> 


40 






















o 


to 


CO 


00 


00 


■^ 


t^ 


to 


to 


to 


lO 


IC 


Tfi 


ni 


T(i 


CO 


Q 




















m 






in 


^ 


s 


o 




















o 








CO 


t^ 


^ 


« 


to 


to 


w 


w 


^ 


■* 


Tti 


CO 


CO 


<N 


o 












^ 


§ 






s 


^ 






^ 










© 


to 






OS 










t^ 


vi 


«d 


to 


ifl 


IC 


•* 


Tti 


«o 


CO 


CO 


c<i 


(N 


^ 









^ 


'P 


in 




m 


g 




in 




rr 




o 
















en 








t^ 






^ 


«> 


lO 


IC 


ic 


-* 


T)< 


CO 


CO 


CO 


^ 


IM 


'^ 


^ 


o 


Q 




<^l 




<-) 


m 




lO 


^ 


05 


to 


o 


m 


lO 


^ 


° 






t- 




















Tf 




lO 


Irt 


•^ 


-* 


00 


CO 


« 




<N 


^ 


-" 


O 


® 


o 


1 '^ 


























































































•^ S&H 








V. 














































o 


= g « 












tu 


to 






OJ 


UJ 




































h5 































STEAM ENGINEERS AND ELECTRICIANS. 155 

would otherwise be wasted, a very material 
economy is effected in the consumption of fuel. 

A pound of feed - water entering a steam 
boiler at a temperature of 50° Fahr., and evapo- 
rating into steam of 60 pounds pressure, requires 
as much heat as would raise 1157 pounds of water 
1 degree. A pound of feed- water raised from 50° 
Fahr. to 220° Fahr. requires 170 units of heat; 
which, if absorbed from exhaust- steam passing 
through a heater, would be a saving of 15 per 
cent, in fuel. Feed-water at a temperature of 
200° Fahr., entering a boiler, as compared in 
point of econoni}^ with feed-water at 50° Fahr., 
would effect a saving of over 13 per cent, in fuel; 
and with a well-constructed heater there ought to 
be no trouble in raising the feed-water to a tem- 
perature of 212° Fahr. 

Q. What is the difference between open and 
closed feed-water heaters ? 

A. In closed heaters the exhaust steam passes 
through a series of brass tubes and the water is 
pumped through the space around the tubes into 
the boiler, or the water may be jjumped through 
the tubes and the steam pass around the tubes. 
In the open type, the steam comes in actual 
contact with the water, the latter passing over a 
series of cast-iron or steel pans placed in a chamber 
through which the exhaust steam passes. 



156 



roper's catechism for 




g M .S o 



S =« 2 



STEAM ENGINEERS AND ELECTRICIANS. 



157 




OPEN HEATER,— PITTSBURGH TYPE. 

(Steam enters below the pans at the left and passes out at the top. 
Water enters through the pipe at the top, the flow being regulated by a 
cock which is controlled by the float and rod. The small cylinder at the 
right separates the oil. [See also page 172.] The connection to the pump 
is near the top of the small cylinder. Through an opening in the side 
of the shell the pans, which rotate around a central shaft, may be 
cleaned. Shell and pans of steel.) 



158 ropek's catechism for 

Q. What is the difference in the method of 
installing open and closed heaters ? 

A. In open heaters the pump is placed between 
the heater and the boiler, hence the pump takes 
hot water and must therefore be placed below the 
level of the water in the heater, otherwise the 
water will not follow the plunger. With the closed 
type the water enters the pump cold and is forced 
through the heater into the boiler. 

Q. Why can open heaters not be used with 
injectors ? 

A. Because if the water is heated to a high tem- 
perature, as it should be, in the heater, the injec- 
tor will not work, it requiring moderately cold 
water to condense the steam in the combining 
tube. If the steam in an injector is not con- 
densed the apparatus will refuse to force the water 
into the boiler. 

Q. Which type is, in general, preferable — the 
open or the closed ? 

A. Each has its advantages and disadvantages. 
The closed heater may be located in any conve- 
nient position relative to the pump, while the open 
type must be placed at a higher level than the 
pump, which, as already stated, has to pump hot 
water; the open type is not under pressure (except 
that of the exhaust steam), hence it is lighter and 
cheaper. It is more easily cleaned; it heats the 



STEAM ENGINEERS AND ELECTRICIANS. 159 

water to a higher temperature; its purifying prop- 
erties are better, and it produces no back pressure 
on the engine. On the other hand, the feed-water 
may contain grease which will injure the boiler, 
although it is claimed that by a suitable oil 
separator this may be entirely eliminated. 

Q. What is an economizer ? 

A. It is a device used for heating the feed-water 
by means of the products of combustion of the 
boiler furnace as they pass into the stack. 

Q. How is it constructed ? 

A. The economizer usually consists of a series 
of cast-iron or steel tubes connected at either end 
by headers similar to those used in water-tube 
boilers. The water circulates through the tubes, 
which are placed in the flue connection just at the 
entrance to the stack. 

Q. What fittings should an economizer have ? 

A. As it is virtually a water-tube boiler, it 
should have a blow-off pipe and a safety-valve, 
because if the boiler is not supplying steam as 
usual the water in the economizer tubes will be 
evaporated, producing an excessive pressure. 

Q. For what purpose are economizers generally 
used ? 

A. For the purpose of increasing the capacity 
or efficiency of existing boiler plants. 

Q. Why are they generally not necessary in new 
installations ? 



160 roper's catechism for 

A. Because if the boilers are properly con- 
structed they do not allow much heat to be wasted 
through the chimney. 

Q. What other method of heating the feed- 
water is sometimes used ? 

A. It is heated by the use of condensers in 
connection with the engines. (See "Condensers," 
page 233.) 

FURNACES AND FLUES. 

Q. Can you calculate the strength of a flue by 
the same rules that apply to the shells of boilers ? 

A. No; because the same rules for strength 
of cylinders under pressure from within do not 
apply to those which are subjected to a pressure 
from without. 

Q. If pressure is exerted on the internal or 
external surface of the cylinder, is the effect not 
the same in both cases ? 

A. No; when pressure is exerted within a tube 
or cylinder, the tendency of the strain is to cause 
the tube to assume the true cylindrical form; but 
when pressure is exerted on the outside of the 
tube, the tendency of that pressure is to crush the 
tube or flatten it; as it is a well-known fact that 
iron of any strength when formed into a tube will 
require a much greater strain to tear it asunder 
than it would take to crush it. A thin hoop of 



STEAM ENGINEERS AND ELECTRICIANS. 161 

iron will resist a very great amount of tearing 
force, but if that same hoop or circle be placed as 
a prop under half the weight that was exerted to 
tear it apart, it would be crushed flat. 

Q, What is the difference between external and 
internal strain? 

A. Internal is a tearing strain, while external 
is a crushing strain; and flues and tubes of boilers 
are nothing but a series of props, and a constant 
tendency of the pressure is to flatten the tube or 
flue and cause it to collapse. 

Q. What is a collapse ? 

A. It is the crushing or flattening of a flue by 
overpressure, and is often attended with terrible 
results. 

Q. How do you calculate the strength of flues 
or cylinders subjected to external pressure? 

A. It has been shown by experiment that the 
strength of such cylinders is proportional to the 
square of the thickness of the cylinder and in-, 
versely proportional to the length and to the 
diameter. The formula for collapsing is: 

P= 806,000^, 
la 

where P is the collapsing pressure in pounds per 

square inch, 

I is the length of the cylinder in feet, 

d is the diameter of the cylinder in inches. 

11 



162 roper's catechism for 

Rule for Finding the Collapsing Pressure 
OF A Cylindrical Flue.- — Multiply the square of 
the thickness in inches by the number 80,600. 
Multiply the length of the flue in feet by its 
diameter in inches. Divide the first product by 
the second, and the quotient will be the collaps- 
ing pressure in pounds per square inch. 

Q. If the length of a cylindrical flue is 10 feet, 
its diameter 2 feet, and thickness J inch, what 
will be the collapsing pressure ? 

^ P = ^0^'7^X|X^ = 215 pounds. 

Q. How may long flues be strengthened ? 

A. This may be done in various ways. The 
old method was to rivet rings of angle- or tee-iron 
around the flue at fixed intervals, or to make the 
flue in sections and to join them together b}^ rivet- 
ing on _f\-shaped rings. The modern method is 
to make the entire flue of corrugated iron, which 
not only adds strength, but facilitates expansion 
and increases the heating surface. 

Q. When the flue is stiffened by rings, as de- 
scribed above, how do you calculate its strength ? 

A. By the same rule as that for plain flues, 
except that the length between rings is taken as 
the length of the flue. 

Q. What method is employed in the Galloway 
boiler for strengthening the flues ? 



STEAM ENGINEERS AND ELECTRICIANS. 163 

A. The Galloway tubes, which are conical in 
form and placed within and across the flues, being 
riveted to the sides. 

GRATES. 

Q. What is the simplest form of grate ? 

A. It consists of a series of cast-iron bars 
shaped like beams, supported at either end, and 
so placed as to allow spaces between them for the 
passage of air. 

Q. What points should, in general, be observed 
in grates ? 

A. They should be flat on top and supported, 
but not fixed at the ends, as otherwise the expan- 
sion and contraction will cause them to get out of 
shape. The spaces between the bars should be 
numerous and as large as possible. The width of 
the spaces, however, depends on the kind of coal 
to be used, and in practice varies from f to f inch. 
The height of the grate above the bottom of the 
ashpit should be from 24 to 30 inches, and the 
bars should, in general, be inclined downward to- 
ward the bridge wall, as the fuel may then be 
more easily distributed. The length is limited by 
the distance to which a fireman can throw the 
coal, which is about 6 feet. 

Q. How much coal is generally consumed per 
square foot of grate surface ? 



164 roper's catechism for 

A. This depends on the nature of the draught 
and the kind of coal. For land boilers fired with 
a good quality of anthracite coal, 9 pounds per 
square foot is a fair average. In some boilers 
operating under a light draught the coal con 
sumption is as low as 4 pounds, while in locomo- 
tives using a blast pipe to produce a stron^ 
draught as high as 120 pounds of coal may be 
burned per square foot of grate surface per hour 

Q. How much grate surface should be alloweu 
per horse-power ? 

A. In land boilers about J square foot of grat^ 
surface is given per horse-power. With good biti^ 
minous coal, better results are obtained by usin 
a smaller grate area and a strong draught. Wit.^ 
coal containing a high percentage of ash it i-^ 
better to use a large grate surface with a compara- 
tively slow rate of combustion. 

Q. What is a shaking grate ? 

A. It is a grate designed for cleaning the fire 
breaking up clinkers, and removing them withou': 
opening the fire door. 

Q. What are the advantages to be derived from 
such an arrangemxcnt? 

A. Whenever the fire doors are opened cold air 
rushes in, tending not only to impair the efficiency 
of the boiler, but also its durability. Moreover, 
it is impossible for a fireman to thoroughly stir 



STEAM ENGINEERS AND ELECTRICIANS. 165 

out, with a slicing-bar, every part of the grate. 
Hence, if the coal has a tendency to form cUnkers 
the advantages of a shaking grate would be 
material. 

Q. AVhat is meant by automatic stoking ? 

A. A system by Which the coal is fed to, and 
the ashes removed from, the furnace automatically 
without opening the furnace doors. 

Q. How long have automatic or mechanical 
stoking devices been in use ? 

A. A device similar in many respects to the 
modern mechanical stokers was employed by 
Watt in 1785. 

Q. Under what conditions are mechanical 
stokers especially desirable? 

A. When the fuel used consists of mine refuse, 
screenings, or other materials not generally used 
in manual firing. 

Q. What advantages are claimed for mechanical 
stokers ? 

A. Fuel economy, prevention of smoke, saving 
*fin labor, and cleanliness in the boiler room. 
^, Q. Why is mechanical stoking productive of 
economy in the use of fuel? 

A. Because the coal is spread upon the grate 
uniformly and at the time when it is needed. 
With hand-firing the coal is fed to the furnace at 
irregular intervals, and usually more coal is put 



166 koper's catechism for 

on than necessary. Besides, each time the boiler 
is fired and cleaned, the furnace doors are opened 
and cold air rushes in. All of these features 
which attend hand-firing are injurious to the 
economy of operation. With a system of mechan- 
ical stoking they are not inciirred, and hence the 
efficiency may be materially increased. 

Q. Why do mechanical stokers lessen the pro- 
duction of smoke? 

A. Because the fuel is fed uniformly in small 
quantities instead of intermittently and in bulk, 
as in the case of hand-firing. A uniform tem- 
perature is maintained in the furnace, and the 
motion of the grate keeps the spaces open for the 
continual passage of the air. Hence the combus- 
tion is at all times complete, which means absence 
of smoke. 

Q. Why are they productive of saving in labor ? 

A. Because there is no cleaning of fires or 
manual labor of any kind, except, perhaps, the 
bringing of the coal to the hoppers; and even this 
is frequently accomplished by machinery. 

Q. Why are they more cleanly ? 

A. Because the usual dirty appearance of boiler 
plants is produced by the dust raised in shoveling 
the coal, cleaning the fires, and removing the 
ashes, all of which operations are abolished in 
mechanical stoking. 



STEAM ENGINEERS AND ELECTRICIANS. 167 

Q. Do mechanical stokers pay in small plants ? 

A. No, they do not; because the cost of the 

plant and the power consumed in operating would 

not be warranted by the saving which w^ould 

accrue. 

CHIMNEYS AND STACKS. 

Q. What is the object of a chimney or stack? 

A. It is for the purpose of producing a draught, 
ejecting the products of combustion, and supply- 
ing fresh air for the combustion of the fuel. 

Q. How does a chimney produce a draught ? 

A. The tendency of the rarefied gases is to rise, 
producing a partial vacuum which causes a rush 
of air through the furnace. 

Q. Which kinds of coal require the tallest 
stacks ? 

A. Anthracites, because they do not burn as 
readily as bituminous coals. 

Q. On what does the draught produced by a 
chimney depend? 

A. It depends on two factors: on the height of 
the chimney and on the difference in weight of 
the gases contained in the chimney and the atmos- 
phere. 

Q. On what does this difference in weight 
largely depend? 

A. Upon the temperature of the gases leaving 
the boiler. 



168 roper's catechism for 

Q. At what temperature do the gases usually 
leave in well-designed boilers ? 

A. 500 to 600 degrees Fahrenheit. 

Q. At what temperature of the escaping gases 
is the best draught obtained ? 

A. At about 580 degrees Fahrenheit. 

Q. On what does the area of the chimney for a 
given boiler plant depend ? 

A. It depends upon the quantity of coal con- 
sumed. 

Q. What relation is there between the quantity 
of coal consumed and the area of the chimney ? 

A. The area of the cross-section in square 
inches should be from 1 J to 2 times the number 
of pounds of coal consumed per hour. 

Q. According to this rule, what would be the 
proper diameter of chimney for 500 horse-power 
boilers of the water-tube type ? 

A. Assuming an evaporation of 10 pounds of 
water under normal conditions per pound of coal, 
we have: 

Pounds of water evaporated per pound of 

coal = 10. 
Total pounds of water evaporated per hour 

= 30 X 500 = 15,000. 
Pounds of coal consumed per hour 

= '±'^ = 1500. 



STEAM ENGINEERS AND ELECTRICIANS. 169 

Area of chimney = 1500 X IJ to 1500 X 2 

= 2250 to 3000 square inches. 
Diameter of chimney = 53J to 61f inches 
or, say, 60 inches. 
Q. What is the relation between grate and 
chimney area? 

A. A fair average of coal consumed per square 
foot of grate surface for anthracite coal is 12 
pounds. Hence the chimney area being about If 
square inches per pound of coal, we have: 

Chimney area per pound of coal = If square 

inches. 
Chimney area per square foot of grate surface 
= lfXl2 = 21 square inches = -^-^^ 
= I square foot ; 
or, in other words, the chimney area should be 
about Y of the grate area. 

Q. Is there any relation between the cross-sec- 
tion of chimney and horse-power ? 

A. For fire-tube boilers the average heating 
surface is 12 square feet per horse-power, while the 
ratio of grate to heating surface is about 1 : 35. 
Hence the grate surface per horse-power may be 
taken roughly as -g-f , or about J. If, now, we take 
the results above, we have for the chimney area 
per horse-power, J X y = ar ^^^ fire-tube boilers, 
and a trifle smaller, say ^V? ^^i' water-tube boilers. 
Q. What determines the height of chimneys ? 



170 



roper's catechism for 



•saqDui 

8:^BniixoaddY jo 
ajBiibs JO apis 


2Sg5SS5g??^^^^SgSg^§g 


'Baay [Binoy 


1.77 
2.41 
3.14 
3.98 
4.91 
5.94 
7.07 
8.30 
9.62 
12 57 
15.90 
19.64 
23.76 
28.27 
33.18 
38.48 
44.18 
50.27 


•J98J SJBllbg 

'uajy 8Aip8jaa 


0.97 
1.47 

2.08 
2.78 
3.58 
4.47 
5.47 
6.57 
7.76 
10.44 
13 51 
16.98 
20.83 
25.08 
29.73 
34. 76 
40.19 
46.01 


i 

o 

H 

w 
o 




§3 

i 

o 

is 

a 
s 

a 


§!igii 


748 
918 
1105 
1310 
1531 
1770 
2027 


d 


iisiiiii 


d 


389 
503 
632 
776 
934 
1107 
1294 
1496 
1720 


d 

o 


271 
365 
472 
593 
728 
876 
1038 
1214 
1415 
1616 


d 
1 


182 
219 
258 
348 
449 
565 
694 
835 
995 
1163 
1344 
1537 


d 

o 

C3 


^amimnm 


d 
8 


SS8||||g^|| 


d 


^^s*il^«S 


d 
S 


s?§sf2g;2^ 


g 


?aS^^S 


ni 


saqduj 


la 


s?5 5;?5g?§sg^^^gg^S3gg 



STEAM ENGINEERS AND ELECTRICIANS. 



171 



A. The height of chmmeys is determined by 
the required draught. It is influenced by the 
kind of coal to be burned as well as by its loca- 
tion, as it must, in general, be higher than hills 
or buildings in the immediate vicinity. 



STEAM SEPARATOES AND TRAPS. 

Q. For what purpose are steam separators used ? 

A. For removing moisture from steam before 
it enters the engine cylinder; or they may be used 
for extracting other liquids from 
vapors, as, for example, the oil 
contained in exhaust steam. 
The first named is generally 
called a live steam separator. 

Q. Why should it be advis- 
able to extract the entrained 
water from steam before using 
it in the engine? 

A. Because an accumulation 
of water in the cjdinder is often 
the cause of blowing out the head 
of the cylinder or steam-chest 
cover; and also because the 
presence of moisture in steam re- 
duces the economy of the engine. 

Q. How should a separator be 
constructed to be efficient ? 




172 roper's catechism for 

A. The steam entering the apparatus at a high 
velocity should have its direction of flow altered 
or reversed, so as to destroy the momentum of 
the liquid particles, permitting them to fall by 
gravity into a vessel provided for that purpose. 
This being accomplished, the steam should not 
again come in contact with the water, as it is 
liable to pick up particles of an}^ liquid with 
which it comes in contact. Finally, the cross- 
section for the passage of the steam should be 
ample in all parts of the apparatus, so that the 
losses by friction will be reduced to a minimum. 

Q. For what other purpose are separators fre- 
quently used ? 

A. To extract the oil from feed-water in open 
heaters. 

Q. How are these constructed ? 

A. In various ways. In the Pittsburgh heater, 
illustrated on page 157, the separation of oil is 
accomplished by means of a small cylinder placed 
on the side of the apparatus near the bottom. 
This cylinder is connected by pipes to the steam- 
and water-spaces of the heater, as shown in the 
cut; the feed to the pump is at the top of the 
small cylinder. As the oil floats on the surface 
of the water it is evident that none will find its 
way into the small cylinder, so long as the water 
is maintained at its proper level, while if the 



STEAM ENGINEERS AND ELECTRICIANS. 173 

level of the water should become too low the 
pump will not be supplied with water. 

Q. For what purpose are steam traps used ? 

A. For the purpose of removing condensed 
steam from a system of steam piping, without 
allowing any of the steam itself to escape. 

Q. How is this accomplished ? 

A. The trap is connected to the piping to be 
drained and contains an outlet controlled by a 
valve. The valve in some traps is operated by a 
float, and in others by means of a bent tube of 
elliptical cross-section. In the former the opening 
and closing of the valve is determined directly by 
the amount of water in the trap. In the curved- 
tube system the opening and closing of the valve 
depend upon the temperature. 

Q. Suppose a separator, trap, heater, or other 
appliance should require cleaning or repairing, 
will it not be necessary to shut down the plant ? 

A. No; they should always be provided with 
by-passes for both steard and water, that is, they 
should be connected with the piping in such a 
way that the steam or water may be made to pass 
temporarily through auxiliary pipes around the 
heater trap or other appliance. 

Q. Give a brief description of the manner in 
which a by-pass is usually constructed. 

A. As generally constructed a by-pass consists 



174 



ROPER'S CATECHISM FOR 



of a pipe leading around the appliance and fitted 
with three valves — V, V„ and V,„ — as shown in 
the accompanying cut, the trap (in this case) 
being connected to the piping by pipe unions U, 
U. Under ordinary conditions, that is, when the 
trap is in operation, the valves V, and V„ remain 
open while V,„ is closed. If, however, the trap 
is to be taken out for any reason, it is only neces- 




sary to close the valves V, and V„ and to open 
y ,,,. The steam, instead of passing through the' 
trap, will then pass around it through the by-pass, 
and the trap or other appliance may be discon- 
nected by means of the two unions U, U, without 
in any way interfering with the operation of the 
plant. For feed- water heaters, etc., a similar 
by-pass should be provided for the water. 



STEAM ENGINEERS AND ELECTRICIANS. 175 



THE STEAM ENGINE. 

The steam engine, as it exists to-day, may be said 
to be the invention of James Watt. While he 
was not the originator of the idea of utilizing the 
pressure and expansive force of steam for the 
purpose of doing mechanical work, Watt's dis- 
coveries and inventions, in this connection, were 
of such importance that he is generally considered 
as the inventor of the steam engine. 

In looking over the models of engines and 
accessories of James Watt, a great many of which 
are exhibited in the South Kensington Museum, 
London, it is surprising to note how little change 
the steam engine has undergone during the past 
century. It is to-day, in fact, the same machine 
that it was then; and while the results which have 
since been accomplished in the way of economy, 
regulation, speed, and power doubtless exceed the 
most sanguine expectations of the early workers 
in this field, the modern engine is, nevertheless, 
practically the same machine that it was a century 
ago. 

The efforts of steam engineers, since the days of 
James Watt, have produced not only vastly more 
powerful machines, higher and more uniform 
speed and what now seems perfect running, but 



176 eoper's catechism for 

they have also very materially increased the effi- 
ciency of the engine. And yet the results which 
have been obtained in the way of economy still 
leave much to be desired. The steam engine and 
boiler, considered as an apparatus for converting 
the potential energy contained in coal or other 
fuel into mechanical work, is a most extravagant 
machine. With the very best engines and boilers 
we are not able to develop a horse-power with a 
consumption of much less than 3 pounds of coal 
per hour, while if all of the energy were utilized 
we should obtain from that amount of good coal 
not less than 14 horse-power. In other words, 
the best engines and boilers utilize only about 7 
per cent, of the latent energy of the fuel. As far 
as the engine itself is concerned, the mechanism 
leaves but little to be desired. In such engines as 
are generally used for electric lighting, that is, the 
high-speed automatic cut-off type, the regulation 
is such that the full load may be suddenly thrown 
on or off without producing a variation in the 
speed of the engine greater than 1 to 2 per cent., 
and at all loads such engines, when properly 
adjusted, run smoothly, noiselessly, and without 
producing vibration. 



STEAM ENGINEERS AND ELECTRICIANS. 177 

HORSE-POWER. 

Q. What is meant by the power of a steam 
engine ? 

A. The amount of work it will do in a given 
space of time. 

Q. Define the unit of power. 

A. The unit generally adopted for the power of 
steam engines is the horse-poiver. An engine of 1 
horse-power means one which will raise 550 
pounds 1 foot a second or its equivalent. 

Q. What would be equivalent to this amount 
of work? 

A. As work is the product of force times space, 
a weight of 550 pounds raised 1 foot would be 
equal to 550 foot-pounds of work. If 1 pound 
were raised 550 feet' or 2 pounds 275 feet, the 
amount of work would be the same. Hence, a 
horse-power may be defined as 550 foot-pounds 
per second, 33,000 foot-pounds per minute, 1,980,- 
000 foot-pounds per hour, and so on. 

Q. Name some form of work other than raising 
a weight, which would be equivalent to 1 horse- 
power. 

A. An electric current of 10 amperes at 74.6 
volts. 

Q. What determines the horse-power of a steam 
engine ? 
12 



178 roper's catechism for 

A. The diameter of the cylinder, length of 
stroke, average or mean effective pressure on the 
piston, and the speed. 

Q. How do you calculate the horse-power of an 



engme 



A. By multiplying the area of the piston in 
square inches by the mean effective pressure acting 
upon it; multiplying the length of stroke in feet 
by the number of strokes (twice the number of 
revolutions) per minute; multiplying the first 
product by the second, and dividing by 33,000. 

Q. What would be the horse-power of an 18" x 

18" engine at 200 revolutions per minute, with a 

mean effective pressure of 45 pounds per sq. inch ? 

A. Area of piston = 18 X 18 X .7854 = 254 

square inches, 

Total mean pressure on piston = 254 X 45 

= 11,430 pounds. 
Number of strokes per minute = 2 X 200 

= 400, 
Length of stroke = 18 -f- 12 ^ 1.5 feet, 
Distance traveled by piston per minute = 

400 X 1.5 = 600 feet, 
Work done per minute =^ 11,430 X 600 = 

6,858,000 foot-pounds, 
Horse-power = 6,858,000 -- 33,000 = 208. 
Q. How would you write the above rule in the 
shape of a formula ? 



STEAM ENGINEERS AND ELECTRICIANS. 179 

A. Let HP = horse-power, 

P = mean effective pressure in pounds 

per square inch, 
L = length of stroke in feet, 
A = area of piston in square inches, 
N = number of strokes per minute, 
B = number of revolutions per min- 
ute, 
S = piston speed in feet per minute, 
d 7= diameter of cylinder in inches; 
the formula corresponding to the above rule would 
be: 

(A = .7854cP) 

PLAN APS 
33,000 ^^ 33,000' 

Q. Given the horse-power, mean effective pres- 
sure, and piston speed, how would you find the 
proper diameter of cylinder? Give rule and 
formula. 

A. The formula would be 



, I 42,017 HP ^„_ I 
d = ^J — '—~ or 205 ^'- 



HP 

PS ^^ "^^ ^ PS 



and the rule as follows : Multiply the horse-power 
by 42,017; multiply the piston speed by the 
mean effective pressure; divide the first product 
by the second and extract the square root of the 
quotient. 



180 eoper's catechism for 

Q. Write formulse for length of stroke, piston 

speed, and number of revolutions when the other 

quantities are given. 

, J ,. , , , r ^3,000 HP 

A. Length ot stroke = L = — ' , ,^ = 
^ FAN 

16,500 HP _ 21,010 H P 
PAR ~ P RcV ' 
Piston speed = S=NL = 2RL = 
33,000 HP 



PA ' 

Number of revolutions = R = 

16,500 HP _ 21,010 HP 
PAL ~ PLd' 



S 
2L 



Q. What do you understand by the mean effec- 
tive pressure ? 

A. The average forward pressure on the piston 
less the back pressure. 

Q. What is the average forward pressure ? 

A. It is a pressure depending upon the initial 
pressure in the cylinder and the point of cut-off. 

Q. How do you find the average (forward) 
pressure in a given case ? 

A. In the following table look up the multiplier 
corresponding to the cut-off. To the initial gauge 
pressure in the cylinder add 14.7 pounds to ob- 
tain the initial absolute pressure. Multiply this 
by the number corresponding to the cut-off in the 



STEAM ENGINEERS AND ELECTRICIANS. 



181 



table, and the product will be the absolute average 
forward pressure. 

Q. What would be the average pressure corre- 
sponding to 80 pounds initial by the gauge and J 
cut-off? 

A. 80 + 14.7 = 94.7 X .5965 = 56.45 absolute 

14.7 



41.75 gauge. 



TABLE 

OF MULTIPLIERS FOR MEAN ABSOLUTE PRESSURES. 



Cut-Off. 


Rate of 
Expan- 
sion. 


Multi- 
plier. 


Cut-Off. 


Rate of 
Expan- 
sion. 


Multi- 
plier. 


1 


4 
3 

2.66 
2 


.5965 
.6995 

.7428 
.8465 


1 

i 
f 


1.6 
1.5 
1.33 
1.14 


.9188 
.9370 
.9657 
9919 



Q, How do you find the mean effective pressure? 

A. Find the absolute mean forward pressure as 
described above and deduct the absolute back 
pressure. 

Q. What is the back pressure? 

A. It is the pressure opposing the piston. In 
engines exhausting into the atmosphere it is 



182 roper's catechism for 

usually about 15 pounds per square inch (atmos- 
pheric pressure). In condensing engines it varies 
from two (2) pounds per square inch up to at- 
mospheric pressure, depending on the vacuum. 
Where the exhaust is used in a heating system, it 
varies from 16 to 25 pounds, depending on the 
amount of friction in the piping. 

Q. What horse-power would be developed by 
an engine under the following conditions: 
Stroke, 12 inches; 
Diameter of cylinder, 12 inches; 
Initial gauge pressure, 80 pounds per square 

inch; 
Speed, 300 revolutions per minute; 
Back pressure (gauge), 5 pounds per square 

inch; 
Cut-off, 1. 
A. The absolute initial pressure is 80 + 14.7 = 
94. 7 pounds, and the multiplier in the table cor- 
responding to \ cut-off being .5965, the average 
forward pressure is 94.7 X .5965 = 56.45 pounds 
absolute. The back pressure being 5 -f- 14.7 = 
19.7 pounds absolute, the mean effective pressure 
is 56.45 — 19.7 = 36.75 pounds per square inch. 
Area of piston = 12 X 12 X .7854 = 113.1 

square inches. 
Total mean pressure on piston = 36.75 X 
113.1 =4153 pounds. 



STEAM ENGINEERS AND ELECTRICIANS. 183 

Length of stroke :=12-v-12 = l foot. 
Number of strokes = 300 X 2 = 600 per 

minute. 
Distance traveled by piston = 600 X 1 ^= 

600 feet per minute. 
Work done per minute = 600 X 4153 == 

2,491,800. 
Horse-power = 2,491,800 -- 33,000 = 75 
horse-power. 
Q. If in the above example, instead of exhaust- 
ing against a back pressure, a condenser had been 
used, in which there was a vacuum of 22 inches, 
what would have been the gain in power ? 

A. Since each inch of vacuum corresponds to 
about |- pound, the back pressure would be 22 X 
^ == 11 pounds less than atmospheric, or 14.7 — 
11 = 3.7 pounds absolute. Hence the mean 
effective pressure = 56.45 — 3.7 = 52.75 pounds, 

.,. T 52.75X113.1 X600 ,^^ 
and the horse-power ^ = 108. 

That is, the gain in power would be 108 — 75 = 
33 horse-power, or over 40 per cent. 

• EXPLANATION OF TABLE. 

The table on the following pages is calculated 
for different cylinder diameters from 4 inches to 5 
feet and for piston speeds of 300 to 600 feet per 
minute. To find the horse-power of any engine 



184 



roper's catechism for 



TABLE 

OF HOESE POWEE FOR DIFFERENT CYLHSTDEE DIAMETERS 
AND PISTON SPEEDS. 

Horse-Power per Pound Mean Effective Pressure. 



2'«'^ 


Speed of Piston in Feet per Minute. 


s 5 


300 


350 


400 


450 


500 


550 


600 


Inches. 
















4 


.114 


.133 


.152 


.171 


.19 


.209 


.228 


4>^ 


.144 


.168 


.192 


.216 


.24 


.264 


.288 


5 


.18 


.21 


.24 


.27 


.30 


.33 


.36 


5>^ 


.216 


.252 


.288 


.324 


.36 


.396 


.432 


6 


.256 


.299 


.342 


.385 


.428 


.471 


.513 


6K 


.807 


.391 


.409 


.461 


.512 


.563 


.614 


7 


.348 


.408 


.466 


.524 


.583 


.641 


.699 


"ly, 


.401 


.468 


.534 


.602 


.669 


.735 


.802 


8 


.456 


.532 


.608 


.685 


.761 


.837 


.912 


8>^ 


.516 


.602 


.688 


.774 


.86 


.946 


1.032 


9 


.577 


.674 


.770 


.866 


.963 


1.059 


1.154 


9J^ 


.644 


.751 


.859 


.966 


1.074 


1.181 


1.288 


10 


.714 


.833 


.952 


1.071 


1.390 


1.309 


1.428 


10^ 


.787 


.919 


1.050 


1.181 


1.313 


1.444 


1.575 


11 


.864 


1.008 


1.152 


1.296 


1.44 


1.584 


1.728 


113^ 


.943 


1.1 


1.257 


1.414 


1.572 


1.729 


1.886 


12 ^ 


1.025 


1.195 


1.366 


1.540 


1.708 


1.880 


2.050 


13 


1.206 


1.407 


1.608 


1.809 


2.01 


2.211 


2.412 


14 


1.398 


1.631 


1.864 


2.097 


2.331 


2.564 


2.797 


15 


1.606 


1.873 


2.131 


2.409 


2.677 


2.945 


3.212 


16 


1.827 


2.131 


2.436 


2.741 


3.045 


3.349 


3.654 


17 


2.054 


2.396 


2.739 


3.081 


3.424 


3.766 


4.108 


18 


2.312 


2.697 


3.083 


3.468 


3.854 


4.239 


4.624 


19 


2.577 


3.006 


3. 436 


3.865 


4.295 


4.724 


5.154 


20 


2.855 


3.331 


3.807 


4.265 


4.7r9 


5.234 


5.731 


21 


3.148 


3.672 


4.197 


4.722 


5.247 


5.771 


6.296 


22 


3.455 


4.031 


4.607 


5.183 


5.759 


6.334 


6.911 


23 


3.776 


4.405 


5.035 


5.664 


6.294 


6.923 


7.552 


24 


4.111 


4.797 


5.482 


6.167 


6.853 


7.538 


8.223 


25 


4.461 


5.105 


5.948 


6.692 


7.436 


8.179 


8.923 


26 


4.826 


5.630 


6.435 


7.2.39 


8.044 


8.848 


9.652 


27 


5.199 


6.066 


6.932 


7.799 


8.666 


9.532 


10.399 


28 


5.596 


6.529 


7.462 


8.395 


9.. 328 


10.261 


11.193 


29 


6.006 


7.007 


8.008 


9.009 


10.01 


11.011 


12.012 



STEAM ENGINEERS AND ELECTRICIANS. 



185 



Horse-Power per Pound Mean Effective Pressure. 



I..I 




Speed of Piston in Feet per Minute. 




2 o = 

5 5 


300 


350 


400 


450 


500 


550 


600 


Inches. 
















30 


6.426 


7.497 


8.568 


9.639 


10.71 


11.781 


12.852 


31 


6.865 


8.001 


9.144 


10.287 


11.43 


12.573 


13.716 


32 


7.308 


8.526 


9.744 


10.962 


12.18 


13.398 


14.616 


33 


7.770 


9.065 


10.360 


11.655 


12.959 


14.245 


15.54 


34 


8.238 


9.611 


10.984 


12.357 


13.73 


15.103 


16.476 


35 


8.742 


10.199 


11.656 


13.113 


14.57 


16.027 


17.484 


36 


9.252 


10.794 


12.336 


13.878 


15.42 


16.962 


18.504 


37 


9.774 


11.403 


13.032 


14.861 


16.29 


17.919 


19.548 


38 


10.308 


12.026 


13.744 


15.462 


17.18 


18.898 


20.616 


39 


10.86 


12.67 


14.48 


16.29 


18.1 


19.91 


21.62 


40 


11.424 


13.328 


15.232 


17.136 


19.04 


20.944 


22.848 


41 


12.006 


14.007 


16.008 


18.009 


20.00 


22.011 


24.012 


42 


12.594 


14.693 


16.792 


18.901 


20.99 


23.089 


25.188 


48 


13.20 


15.4 


17.6 


19.8 


22.0 


24.2 


26.4 


44 


13.818 


16.121 


18.424 


20.727 


23.03 


25.333 


27.636 


45 


14.454 


16.863 


19.272 


21.681 


24.09 


26.339 


28.908 


46 


15.128 


•17.626 


20.144 


22.662 


25.18 


27.698 


30.216 


47 


15.768 


18.396 


21.024 


23.652 


26.28 


28.908 


31.536 


48 


16.446 


19.187 


21.928 


24.669 


27.41 


30.151 


32.152 


49 


17.142 


19.999 


22.856 


25.713 


28.57 


31.427 


34.284 


50 


17.85 


20.825 


23.8 


26.775 


29.75 


32.725 


35.7 


51 


18.54 


21.665 


24.76 


27.855 


30.95 


34.045 


37.08 


52 


19.296 


22.512 


2.5.728 


28.944 


32.16 


35.376 


38.592 


53 


20.052 


23.394 


26.736 


30.078 


33.42 


36.762 


40.104 


54 


20.82 


24.29 


27.76 


31.23 


34.7 


38.17 


41.64 


■ 55 


21.594 


25.193 


28.792 


32.391 


35.99 


39.589 


4.3.188 


56 


22.386 


26.117 


29.848 


33.579 


37 31 


41.041 


44.772 


57 


23.196 


27.062 


30.928 


34.794 


38.66 


42.526 


46.392 


58 


24.018 


28.021 


32.024 


36.027 


40.03 


44.033 


48.036 


59 


24.852 


28.994 


33.136 


37.278 


41.42 


45.562 


49.704 


60 


25.698 


29.981 


34.264 


38.547 


42.83 


47.113 


51.396 



by means of this table, multipl}^ twice the number 
of revolutions per minute by the length of stroke 
in feet. This will give the piston speed in feet 
per minute. Look up the horse-power from the 



186 koper's catechism for 

table for this piston speed and the proper diameter 
of cyHnder and multiply it by the mean effective 
pressure. Take the above example as an illustra- 
tion; the piston speed was found to be 600 feet 
per minute, and hence for a 12-inch cylinder the 
horse-power from the table is 2.05 for each pound 
of mean effective pressure. Hence multiplying 
this by the mean effective pressure, 52.75, we have 
52.75 X 2.05 = 108 horse-power. 

Q. Is the pressure in the boiler and the pressure 
in the cylinder nearly equal in all cases ? 

A. No; the pressure in the C3dinder is in many 
cases less than the pressure in the boiler. 

Q. From what causes does the difference between 
the pressure in the boiler and the pressure in the 
cylinder arise ? 

A. Firsts from a malconstruction of the steam- 
pipe and steam-ports; secondly^ from loss by radi- 
ation and condensation; thirdly^ from the action of 
the governor; and, fourthly^ from the bad condition 
of the piston. 

Q. What is the most economical steam pressure 
to use in the cylinder of a high-pressure engine ? 

A. From 80 to 90 pounds to the square inch. 

Q. Why should 80 or 90 pounds to the square 
inch be more economical than lower pressure, say 
40 or 45 pounds to the square inch ? 

A. On account of the back pressure of the 



STEAM ENGINEERS AND ELECTRICIANS. 187 

atmosphere; for instance, if we have a pressure 
of 45 pounds to the square inch on the piston, 
the loss by atmospheric pressure is 15 pounds to 
the square inch, which is about J- of the pressure 
on the piston, leaving only 30 pounds for useful 
effect and to overcome the friction of the engine; 
if Ave have a pressure of 90 pounds to the square 
inch, the loss is only 15 pounds to the square inch, 
or about ^. 

Q. Is it economical to use an engine that is too 
large for the work to be done ? 

A. No; because an engine running below its 
rated load wastes steam. If it is a throttling 
engine^ the steam is throttled, or reduced without 
doing work, which means a loss. If it is an 
automatic cut-off engine the expansion is increased, 
which also impairs the economy of the engine. 

Q. Why does increasing the rate of expansion 
reduce the economy ? 

A. There is one point of cut-off which is more 
economical than any other, because at that point 
the steam expands to atmospheric pressure and is 
not capable of doing any more w^ork when ex- 
hausted. This cut-off, for an initial pressure of 
80 pounds, is J. If the rate of expansion is 
reduced, the steam is exhausted before it has done 
as much work as it is capable of doing, while if 
the rate of expansion is increased, the terminal 



188 roper's catechism for 

pressure is liable to fall below that of the atmos- 
phere, in which case the opposing pressure of 
the atmosphere will retard the piston during the 
latter part of its stroke. This also means a waste 
of power. 

DIFFERENT KINDS OF ENGINES. 

Q. What is the difference between condensing 
and non-condensing engines ? 

A. In non-condensing engines the steam, after 
having done its work in the steam cylinder, escapes 
into the atmosphere, or sometimes into a heating 
system where the heat still contained in the steam 
is partially utilized. In the condensing engine 
the steam exhausts into a condenser, where it 
comes in contact with some cooling medium, in 
consequence of which it is condensed, producing 
a partial vacuum behind the piston. 

Q. What is the object of condensing? 

A. To increase the effective pressure on the 
piston and consequently the power. 

Q. By how much is the power of a non-con- 
densing engine increased when a condenser is 
added? 

A. The power is increased in the ratio which 
the vacuum in the condenser bears to the mean 
effective pressure. 

Q. Suppose an engine working at 80 pounds 



STEAM ENGINEERS AND ELECTRICIANS. 189 

initial pressure and J cut-off exhausting against 
the atmosphere, had a condenser added. If there 
were an effective vacuum of 26 inches, what would 
be the percentage increase m power if the speed 
remained the same ? 

A. According to the rules given above, the mean 
effective pressure was originally 

(80 + 14.7) X .5965 — 14.7 = 41.75 pounds, 
which was increased by adding a condenser whose 
vacuum is 26 inches by 

26 -- 2 = 13 pounds. 
Hence the increase in power is 

-— -— =: 31 per cent. 
41.75 ^ 

Q. Does it not require power to operate a con- 
denser ? 

A. Yes; but generally not so much as is gained 
by its use. 

, Q. What percentage is gained in economy by 
condensing? 

A. From 20 to 35 per cent., depending on the 
type and size of engine. 

Q. Why, then, are not all engines built for 
condensing ? 

A. Because in small engines the saving in fuel 
would not be enough to warrant the additional first 
cost, and the increased labor and attention which 
the plant would require. Further, in many in- 



190 eoper's catechism for 

stallations the steam leaving at atmospheric pres- 
sure can be used to good advantage for heating 
purposes or for purifying the water before it enters 
the boiler. Finally, in cities the cost of the water 
is frequently in excess of what would be saved in 
fuel. 

Q. How much water is required for condensing ? 

A. About 25 times as much as passes through 

the engine. 

(See also ' ' Condensers, ' ' page 233. ) 

Q. AVhat do you mean by "simple" or single 
expansion and by multiple expansion engines ? 

A. A simple or single expansion engine is one 
in which the steam is used expansively in one 
cylinder or set of cjdinders only, and after ex- 
hausting is not used again for doing work in the 
engine. In multiple expansion engines the steam 
expands successively, doing work, in two or more 
cylinders or sets of cylinders. 

Q. What are the names given respectively to 
engines in which the steam expands two, three, 
and four times ? 

A. Compound, triple expansion, and quadruple 
expansion engines. 

Q. What is meant by compounding ? 

A. By the term "compounding" is meant 
expanding the steam successively in two or more 
cylinders. 



STEAM ENGINEERS AND ELECTRICIANS. 191 

Q. Why are engines compounded ? 

A. To secure greater economy in the use of 
steam. 

Q. Is not the friction of an engine greater if it 
uses the same amount of steam in two or three 
cylinders than if the entire work is performed in 
a single cylinder ? 

A. Yes; because each cylinder (except in tan- 
dem compound engines) has its own crank and 
attending mechanism. 

Q. Why, then, is expanding successively in 
several cylinders productive of economy in the 
use of fuel ? 

A. The higher the initial steam pressure used 
in a steam-power plant, and the lower the terminal 
pressure (provided it is not less than the back 
pressure), the greater the economy. Hence, in 
order to secure the greatest fuel economy, there 
must of necessity be a wide range of temperature 
from live to exhaust steam. If the expansion 
occurred in a single cylinder, the walls of the latter 
and a portion of the steam passages would be 
subjected to this variation in temperature at each 
stroke. In other words, the cylinder walls and 
steam passages would be chilled at the end of the 
stroke and, therefore, the live steam would be 
partially condensed, as it enters the cylinder, 
without doins: work. It is in reducing this loss 



192 roper's catechism for 

of steam by condensation, called initial condensa- 
tion, that compounding effects economy in fuel, 
because if the expansion occurs successively in 
two cylinders, instead of all in one, the range of 
"•temperature is only one-half as great and con- 
sequently the condensation is reduced proportion- 
ately. 

Q. What should be the relative sizes of cylinders 
in multiple expansion engines ? 

A. They should be so proportioned that approx- 
imately the same amount of work is done by each 
cylinder. The first cylinder will be the smallest 
in diameter and the last the largest. 

Q. What names are given to the different 
cylinders of multiple expansion engines ? 

A. The one which takes the steam direct from 
the boiler is called the high-pressure cylinder, and 
the one in which it expands last before finally 
being exhausted to the atmosphere or condenser 
is called the low-pressure; the others are called 
intermediate-pressure cylinders. 

Q. What is a receiver ? 

A. It is a chamber in which the steam is stored 
from the time it leaves one cylinder until it is 
admitted to the next. 

Q. Why is a receiver necessary? 

A. Because the cranks of the different cylinders 
are usually not placed in the same position. For 



STEAM ENGINEERS AND ELECTRICIANS. 193 

example, in a two- or four-cylinder engine they 
would generally be placed at 90° and in a three- 
cylinder engine at 120°. Hence the cylinders are 
not taking steam during the time it is exhausted 
in the preceding cylinder and, therefore, a chamber 
must be provided for storing the steam until it can 
be used. 

Q. Why are cranks set at different angles ? 

A. To secure a more uniform turning force on 
the crank shaft. 

Q. Does not the fly-wheel accomplish the same 
result ? 

A. Yes; but if this can be done without the aid 
of a fly-wheel it is much better, especially since 
in many instances, such as in marine engines, a 
fly-wheel cannot be conveniently used. 

Q. Why are compound engines operated as con- 
densing engines wherever possible ? 

A. Because the increase in the mean effective 
pressure in the low-pressure cylinder is a large 
proportion of the total. Low-pressure cylinders 
of multiple expansion engines frequently have a 
mean forward pressure of only 3 or 4 pounds, and 
hence by the use of a condenser this may be 
increased very materially. 

Q. What do you understand by a high-speed 
engine ? 

A. Strictly speaking, a high-speed engine is one 
13 



194 roper's catechism for 

which has a high piston velocity; but the term is 
now generally used to mean engines of high rota- 
tive speed. 

Q. What advantages do high (piston) speed 
engines possess as compared to low-speed engines ? 

A. Other things being equal, they are lower in 
first cost, more economical to operate, and run 
more smoothly. 

Q. What additional advantage is possessed by 
high (rotative) speed engines? 

A. They are better adapted for driving electric 
machinery and other shafting which requires to be 
run at a high speed of rotation. 

Q. Why are high-speed engines lower in first 
cost? 

A. The power of an engine depends on the 
piston area, stroke, mean pressure, and speed, 
varying directly as each one of these factors. If 
the speed is increased, any one of the other three 
factors may be proportionately decreased, and, 
therefore, it follows, that a high-speed engine may 
be built smaller and hence more cheaply for a 
given horse-power than a low-speed engine. 

Q. Why are they more economical in the use of 
fuel? 

A. Because one of the principal losses in steam 
engines is that due to initial condensation and 
re-evaporation, and this is the less the more steam 



STEAM ENGINEERS AND ELECTRICIANS. 195 

passes through a given cylinder in a given time. 
Hence it is less in high- than in low-speed engines. 

Q. Why do they run more smoothly ? 

A. Principally because the effect of the recipro- 
cating parts is to equalize the turning force on the 
crank pin, so that it is nearly the same at every 
part of the stroke. 

Q. A¥hat do you understand by automatic cut- 
off and throttling engines ? 

A. Automatic cut-off engines are those in which 
the speed is kept constant under a variable load 
by a governor acting upon the cut-off — that is, one 
in which the steam is admitted longer, for heavy 
loads than for light loads, the exact point at 
which it is cut off being regulated by the governor. 
In the throttling engine, the period of admission 
remains the same under all loads, but the initial 
pressure is regulated by the action of the governor 
on a throttle valve. 

Q. Which of the two is the more economical 
method ? 

A. The automatic cut-off; because when the 
pressure of steam is reduced by a throttle valve, it 
expands without doing work and hence an amount 
of energy is lost equal to that which would be 
necessary to raise the steam from the pressure at 
which it is admitted to the C3dinder to that at 
which it is delivered by the boiler. 



196 roper's catechism for 

Q. Under what conditions could throttling 
engines be used ? 

A. When the load remains uniform or nearly 
so, because throttling engines with plain slide 
valves are simpler and cheaper to build than auto- 
matic cut-off engines. 

Q. What are single- and double-acting engines ? 

A. Single-acting engines are those in which 
steam is admitted on one side of the piston only. 
In double-acting engines it is admitted alternately 
on either side of the piston. 

Q. What are the relative advantages of these 
two types ? 

A. For the same diameter of cylinder, length 
of stroke, steam pressure, and speed, the double- 
acting engine develops twice as much power. The 
single-acting engine, however, has no piston rod, 
cross-head, or guides, the connecting rod being 
attached direct to the piston. Engines of this 
class usually run faster, however, than double- 
acting engines, and they are so arranged that the 
crank dips into a vessel filled with oil, every 
revolution, all of the moving parts being encased 
in an iron boxing. They are, therefore, well 
adapted for use where the atmosphere contains 
much grit and dust. 

Q. What is a rotary engine ? 

A. It is one in which a motion of rotation is 



STEAM ENGINEERS AND ELECTRICIANS. 197 

i produced directly by the pressure of the steam 
and not a reciprocating motion first, which is 
afterward converted into a rotary motion, as in 
the ordinary type. 

VALVES AND VALVE GEAES. 

Q. What do you understand by the valve gear 
of an engine? 

A. All that part of its mechanism which is 
used in the distribution of steam. 

Q. Of what does the simplest form of valve 
gear consist ? 

J.. Of a plain slide valve, an eccentric, and the 
rods or links necessary for transmitting the motion 
of the latter to the former. 

Q. Describe the plain slide valve. 

A. The diagram on page 198 shows the simplest 
form of slide valve in its central position, that is, 
in the position where steam is neither admitted to 
nor exhausted from the engine. V is the valve, 
S S are the steam passages through which steam is 
admitted to the cylinder C from the steam-chest 
X. The latter, being in communication with the 
boiler, is always filled with live steam when the 
throttle valve is open. E is the exhaust passage 
which, being in communication with the exhaust 
pipe, allows the steam to pass into the atmosphere 
or condenser after it has done its work in the 



198 



KOPER'S CATECHISM FOR 




STEAM ENGINEERS AND ELECTRICIANS. 199 

cylinder. R is the valve rod which receives its 
motion from the eccentric and, passing through a 
stuffing-box, imparts motion to the valve. 

Q. Explain briefly the method of action of the 
valve. 

A. As already stated, the valve in the above 
diagram is shown in a position where steam is 
neither admitted to nor exhausted from the 
cylinder. In this position of the valve, the piston 
which has nearly completed its stroke, is moving 
toward the left, while the valve is moving toward 
the right, as indicated by the arrows. Presently 
the valve will have uncovered the left steam pas- 
sage and steam will be admitted behind the piston. 
This will continue until the steam passage is again 
covered by the valve on its return stroke. In the 
meantime the other steam passage will have been 
uncovered and placed in communication with the 
exhaust chamber E, and exhaust will take place 
until this passage is again covered by the valve. 
After that the process is reversed, steam being 
admitted to the right hand end of the cylinder 
and exhausted from the left; and so on, continu- 
ously. 

Q. What are the four important events in the 
steam distribution, which take place in every 
double stroke of the engine ? 

A. Admission, cut-off, release, and compression. 



200 roper's catechism for 

Q. Explain what you mean by these terms. 

A. When the passage is first uncovered admis^ 
sion takes place and continues until the point of 
cut-off is reached, which is when the passage is 
again covered. Release occurs when the passage 
is opened to the exhaust, and compression when 
the latter is closed. From the time steam is cut 
off until it is released expansion takes place. 

Q. What do you mean by the terms lap, lead, 
eccentricity, travel, overtravel, angular advance ? 

A. Outside or steam lap is the distance the outer 
edge of the valve laps over the outer edge of the 
steam passage, in the central position of the valve, 
the distance a h in the cut. 

Inside or exhaust lap is the distance the inner 
edge of the valve laps over the inner edge of the 
steam passage, in the central position of the valve, 
the distance c d in the cut. 

Lead is the amount the steam port is open when 
the piston is beginning its stroke. If the piston 
begins its stroke before the steam passage is 
uncovered the lead is negative. 

Eccentricity, or throw of the eccentric, is the 
distance from the center of the shaft to the center 
of the eccentric. 

Travel of the valve is the total distance it moves 
on its seat between extreme positions. This travel 
is equal to twice the throw of the eccentric. 



STEAM ENGINEERS AND ELECTRICIANS. 201 

Overtravel is the distance the valve travels above 
what is necessary to fully uncover the steam pas- 
sage. 

Angle of advance is the angle by which the 
eccentric is in advance of the position which 
would bring the valve in its central position when 
the crank is on a dead center. 

Q. Having given the various dimensions of a 
valve gear of this kind, how do you determine 
when the events described above will take place ? 

A. Graphically — that is, with the aid of some 
diagram such as Zeuner's, Sweet's, or Reuleaux's. 
Of these, Zeuner's is the one generally used in 
practice. 

Q. Briefly explain the Zeuner diagram and its 
use. 

A. *Draw a line X to represent the crank at 
the beginning of the stroke, and with this as a 
radius draw the crank circle ZX^, Xj, Xg, X^. 
Suppose the crank to turn in the direction of the 
arrow. Through the point draw the line R R^ 
making the angle R Y' equal to the angle of 
advance, and lay off the distances OR and OR 
equal to the eccentricity or throw of the eccentric. 
On the lines R and R as diameters draw the 
two circles C i? Z) and E R F. With as a 
center and a radius A equal to the outside or 

*From "Eoper's Engineers' Handy-Book," pp. 391-393. 



202 



roper's catechism for 



steam lap draw a circle A C D, and similarly with 
a radius B equal to the inside or exhaust lap, 
draw a circle B E F. Through the point and 



J 



ZEUNER DIAGRAM. 



the intersections (7, D, E, and F draw the lines 
X,, Zj, Xg, and X,. We are now able 
to take from the diagram all of the data necessary 



STEAM ENGINEERS AND ELECTRICIANS. 203 

for a complete understanding of the distribution 

of steam in the cylinder: 

X^ is the position of the crank when admission 

of the steam begins. 
X^ is the position of the crank when cut-off 

takes place, hence — 
X^ X^ is the angle traversed by the crank during 

the period of admission. 
-Xg is the position of the crank when the exhaust 

opens. 
X^ is the position of the crank when the exhaust 

closes, hence — 
Xg X^ is the angle traversed by the crank during 

the period of exhaust, and — 
X^ Xj is the angle traversed by the crank during 

the period of compression. 
The distances from the intersection of the circles 
R and R^ with the lines X, X^, etc. , represent 
the travel of the valve corresponding to the posi- 
tions OX, Xj , of the crank. The circle R repre- 
sents the forward and the circle R' the return 
stroke, hence — 
X is the distance the valve has traveled from its 

central position at the beginning of the stroke. 
X', the same for the return stroke. 
^ is the outside or steam lap, hence— 
A K is the distance the steam port is open at the 

beginning of the stroke or the steam lead. 



204 roper's catechism for 

R is the full travel of the valve. 
5 is the inside or exhaust lap, hence — 
B Kis the distance the exhaust port is open at the 
beginning of the stroke or the exhaust lead. 

At the points C and D the travel of the valve is 
just equal to the outside lap; hence in these posi- 
tions of the crank the steam port opens and closes 
respectively; similarly at the points E and F the 
travel is just equal to the exhaust lap; hence, in 
these positions of the crank the exhaust port opens 
and closes respectively. If we lay down from the 
point A a distance A H, equal to the width of the 
port, and with as a center and a radius H 
draw an arc, cutting the line i? at J, — 
J R is the distance the valve travels more than 
enough to fully open the port, or the over- 
travel. 

Similarly, if we lay off from B the distance B L, 
equal to the width of the port, and from the center 
and a radius equal to L draw an arc, cutting 
the line R at M, — 

31 R is the distance the valve travels more than 
enough to fully open the port to the exhaust. 

It will thus be seen that by a careful study of 
the diagram all information necessary for the 
proper design and setting of the valve gear may 
readily be had. For example, in the above dia- 
gram the cut-off takes place a little later than f 



STEAM ENGINEERS AND ELECTRICIANS. 205 

stroke. It is evident that if it is desired to have 
the cut-off take place earUer, say at J stroke, it 
will be necessary for the outside lap circle, A C D^ 
to intersect the valve circle R in the line Y Y. 
This may be accomplished by increasing the out- 
side lap, by reducing the eccentricity, or by chang- 
ing the angle of advance. However, any one of 
these changes would also affect the entire distribu- 
tion, and it would probably be necessary to lay 
down several diagrams before the most advantage- 
ous dimensions could be obtained. 

Q. How would you proceed to set the slide- 
valve of an engine ? 

A. Place the crank on the dead center and give 
the valve the necessary amount of lead ; then turn 
the engine on the other center, and if the valve 
has the same amount of lead it is properly set. 
But if the lead on one end is more or less than on 
the other, the difference must be divided. When 
the valve is attached to the rod by means of jam- 
nuts great care must be taken not to jam the nuts 
against the valve, as that would prevent the valve 
from seating. 

Q. What is a link motion ? 

A. It is a mechanism consisting of two eccen- 
trics and rods and a slotted link, designed for the 
purpose of reversing an engine and varying its 
point of cut-off. 



206 roper's catechism for 

Q. How is this accomplished in the Stephenson 
Imk? 

A. The two eccentrics, called respectively the 
forward and back eccentric, are placed on the shaft 
in different relative positions in such a way that, if 
the valve were operated by the one, the engine 
would move forward; and if by the other, it would 
be reversed. The link is attached to the ends of 
the two eccentric rods and hence receives a rocking 
motion. It is slotted and carries a movable block 
in the slot to which the valve rod is attached. If 
the block is at the end of the link nearest the for- 
ward eccentric, the engine will move forward, 
while if it is at the other end, it will be reversed. 

Q. What happens when the block is in some 
intermediate position? 

A. The travel of the valve becomes less as the 
block approaches the center, and hence the cut-off 
becomes earlier. In the central position of the 
block, the travel of the valve is not sufficient to 
uncover the ports, and hence the engine remains at 
rest. 

Q. In the ordinary form of D slide valve, is 
there not a good deal of friction between the valve 
and its seat ? 

A. Yes; the friction in the old forms of slide 
valve is very great, because the steam pressure on 
the back of the valve forces it tightly against its seat. 



STEAM ENGINEERS AND ELECTRICIANS. 207 

Q. How can this be avoided to a great extent ? 

A. By the use of pressure plates, which relieve 
the back of the valve of its pressure, or by the use 
of the piston valve, which, being of circular cross- 
section instead of flat, is balanced and conse- 
quently the only pressure tending to force it 
against the seat is that due to its own weight.* 

Q. What objection is there to piston valves? 

A. It is claimed that the seat wears unevenly 
and hence they cannot be kept tight. With a 
suitable construction, however, the bushings form- 
ing the seat can be taken out and replaced with 
very little trouble and expense. 

Q. Next to the slide-valve gear, as described 
above, what is the most common valve gear used 
in stationary engines ? 

A. The Corliss gear. 

Q. What are the essential differences between 
the Corliss and the plain slide-valve gear ? 

A. Instead of a single valve which admits and 
exhausts the steam, the Corliss gear has four 
independent valves which rotate partially about 
an axis. The four valves, of which two are for 
the admission and cut-off and the other two for 
the release and compression of the steam in the 
cylinder, are operated by a single eccentric and 
wrist plate, but the two steam valves are connected 

*See "Roper's Engineers' Handy-Book," pp. 398-402. 



208 roper's catechism for 

to the wrist plate in such a way that they can be 
detached at any moment. This is accompHshed 
by a tripping or releasing mechanism controlled 
by a ball governor, and as soon as the steam valves 
are released, they are closed by the action of a 
dash pot, and hence the cut-off is under the direct 
control of the governor. The exhaust valves are 
not released from the wrist plate, and hence the 
release and compression are constant. 

Q. What do you understand by a four-valve 
engine ? 

A. It is one having a valve gear midway between 
the plain slide valve and the Corliss gears. It has 
four independent valves like the Corliss, but, like 
the plain slide valve, their motion is 'positive and 
they have no releasing mechanism. The cut-off 
is varied by the travel of the valve. 

Q. What are the relative advantages and dis- 
advantages of the Corliss and four- valve types of 
valve gear ? 

A. The Corliss has the advantage that the cut- 
off is quick and sharp and that there is very little 
power lost in friction. The valves being, however, 
under the control of a spring or dash pot, they 
cannot be run at a high rotative speed. . This 
constitutes the main advantage of the four-valve 
gear, that it can be run at as high a speed as a 
single-valve engine, and it is almost, but not quite, 



STEAM ENGINEERS AND ELECTRICIANS. 209 

as economical as the Corliss. Both have the ad- 
vantage over single-valve engines that the steam 
enters and leaves the cylinder by separate passages, 
and hence there is less loss by condensation. 
They are, therefore, much more economical in the 
use of steam than single- valve gears. 

GOVERNORS. 

Q. What are the principal methods in use for 
governing the speed of stationary engines ? 

A. By the centrifugal governor acting on the 
throttle valve — that is, by varying the initial pres- 
sure in the cylinder to suit the load ; and by a 
centrifugal or inertia governor acting on the valve 
gear in such a way as to vary the point of cut-off 
to suit the load. 

Q. Which is the better method, and why ? 

A. The one in which the cut-off is varied to 
suit the load, because it is much more economical 
in the use of steam, and the regulation is far 
better. Moreover, engines in which the steam, 
pressure is throttled to suit the load often knock 
violently under light loads. 

Q. Why should the steam never be throttled on 
engines running at a high piston velocity? 

A. Because the force necessary to accelerate the 
reciprocating parts at the beginning of the stroke 
is so great in high-speed engines that if the steam 
14 



210 ROPER^S CATECHISM FOR 




CENTRIFUGAL BALL GOVERNOR. 



STEAM ENGINEERS AND ELECTRICIANS. 211 

. were throttled the fly-wheel would have to supply 
it, and hence there would be a reversal of pressure 
on the crank pin each stroke. This would not 
only cause very noisy running, but it would soon 
wear out the engine. 

Q. How is the governor usually made to vary 
the cut-off? 

A. By a releasing mechanism, as already ex- 
plained above (Corliss valve gear); by the action 
of a ball governor on the block of a link, as in the 
Porter- Allen engine; or by a shaft governor. 

Q. What is a shaft governor ? 

A. It is one in which the centrifugal action of 
a weight or weights, placed in a fly-wheel, is 
balanced against a spring or springs. The weights 
are attached to pivoted arms, and these in turn to 
the eccentric of the valve gear. As the speed 
increases, the tendency is for the weights to move 
away from the shaft and in so doing to alter the 
position of th-e eccentric, varying its angular 
advance or its throw, or both, and in this way 
altering the point of cut-off. 

Q. What is the difference in the effect on the 
steam distribution when the cut-off is varied by 
the angular advance and by the throw of the 
eccentric ? 

A. If the angle of advance only is altered, the 
lead will increase as the cut-off is decreased. If 



212 



ROPER'S CATECHISM FOR 



the throw of the eccentric only is altered, the 
reverse takes place. Hence, in order to keep the 
lead constant with a single valve, both the throw 




SHAFT GOVERNOR,— BUCKEYE TYPE. 

(A A are the weights attached to the ends of arms a a. The arms are 
pivoted to the fly-wheel at one end' and attached to the loose eccentric C 
at the other. FF are the springs which resist the tendency of the weights 
to move away from the shaft. In this type of governor the angular 
advance only is varied.) 

of the eccentric and the angular advance should 
be varied. In the governor illustrated above, 
this is not necessar}^, because a separate valve is 
used to cut off the steam. 



STEAM ENGINEERS AND ELECTRICIANS. 213 

Q. How do you calculate the proper diameter 
for ball-governor pulleys ? 

A. To find the diameter of governor shaft-pul- 
leys : Multiply number of revolutions of engine 
by diameter of engine shaft-pulley, and divide 
product by number of revolutions of governor. 

To find diameter of engine shaft-pulley : Mul- 
tipl}^ number of revolutions of governor by diam- 
eter of governor shaft-pulley, and divide product 
by number of revolutions of engine. 

INSTALLATION, CARE AND MANAGEMENT. 

Q. What is the best material for engine founda- 
tions ? 

A. They should be of hard-burned brick laid 
in Portland cement or of concrete. 

Q. How deep should they be carried ? 

A. The proper depth depends on the size of the 
engine. The builders usually furnish a founda- 
tion plan showing minimum depth, but they 
should always rest on solid ground. 

Q. How should the foundation bolts and anchor 
plates be placed in the foundation ? 

A. A template should first be constructed to 
hold the bolts in their proper positions and the 
bolts suspended from the template. The bolts 
should be threaded at both ends and the lower nut 
held in a suitable pocket in the anchor plate. In 



214 



ROPER'S CATECHISM FOR 



building the foundation a space should be left 
around each bolt, sufficient to allow the bolt to be 
moved a half inch in any direction. 

Q. How should the foundation be finished ? 

A. A cap-stone of granite makes the best finish, 
but, as a rule, the expense is too great. After the 
engine is set on the foundation and leveled by 
means of iron wedges, the space between the 
bottom of the engine and the top of the founda- 
tion should be filled with grout or, preferably, 
molten sulphur, to give an even bearing. 

Q. Should foundations be built the same width 
from bottom and top ? 

A. No; they should be wider at the bottom and 
have a slope or batter of about two inches to every 
foot of height up to the floor-level. The top 
should be about an inch wider than the bed plate 
of the engine. 

Q. How would you proceed to set up an engine ? 

A. First. Determine the position or location 
the engine is to occupy in the shop or factory. 

Second. Lay out the line of the main shafting 
in the building, if there be any; if not, the line 
of the building itself, at, at least, three different 
points in the direction in which the main shafting 
is to run; now line down from the center of the 
main shaft, or from the line of the building, at 
two different points, to the floor on which the 



STEAM ENGINEERS AND ELECTRICIANS. 215 

engine is to stand, and from these points line to 
the engine-shaft.- 

Third. Determine the height the bed-plate is 
to stand above the floor; also the depth of the 
foundation. 

Fourth. Make a template the exact counterpart 
of the bed-plate, in which to hang the foundation 
bolts, and set this upon four props at right angles 
to the main shaft in the building. 

Fifth. Lay up the brick foundation to the level 
at which the engine is intended to stand; then 
remove the template, and lower the bed-plate on 
to the foundation. 

Sixth. Level the bed-plate by means of iron 
wedges and pour in sulphur to give it an even 
bearing. After that the nuts may be screwed 
down on the foundation bolts. 

Seventh. A line should now be drawn exactly 
through the center of the cylinder, and another 
line through the center of the main bearing. 
This line will give the location of the pillow-block 
or outboard bearing. 

Eighth. Place a straight edge across the bottom 
of the bearings and adjust them with the aid of a 
spirit level until they are perfectly level. 

Ninth.. Swing the fly-wheel into its proper 
position, slip the shaft through it and key it in 
place. Screw down the caps of the pillow-blocks. 



216 roper's catechism for 

Tenth. Place the cross-head, connecting rod, 
etc., in position, bolt on the front cylinder head, 
and adjust the valve gear. 

Q. AVhat are the principal points which should 
be kept in mind in running the steam and exhaust 
pipes for an engine ? 

A. They should be run in such a way that the 
free flow of steam will never be impeded. The 
steam- and exhaust-pipes should never be smaller 
than the outlets provided on the engine. The 
pipes should be run as straight as possible. 
Horizontal runs should be slightly inclined to 
allow the condensation to drain of! in the same 
direction as the flow of the steam. The piping, 
if long, should have a suitable provision for 
expansion, and all steam- and exhaust-piping 
should be covered with some non-conducting 
pipe-covering. 

Q. What is the first duty of an engineer in 
regard to the steam engine ? 

A. He should always keep it clean and free from 
rust, oil, and grit. This does not involve a great 
deal of labor, and adds very materially to the life 
of the engine. 

Q. How should an engine be started ? 

A. First see that the drips are all open. The 
cylinder should then be warmed by slightly open- 
ing the throttle. 



STEAM ENGINEERS AND ELECTRICIANS. 217 

Q. How should the clrij^s be left when the 
engine is not running ? 

A. They should be left open so as to allow the 
condensed steam to escape. 

Q. How do you pack stuffing-boxes ? 

A. Before packing the piston- and valve-rods 
all the old packing should be carefully removed. 
The new packing should be cut in suitable lengths, 
and the joints placed at opposite sides of the box. 
The stuffing-box should then be screwed up until 
the leakage around the rod is stopped, and no 
further, as any unnecessary tightening of the 
stuffing-box will greatly diminish the power of 
the engine and soon destroy the packing by the 
increased friction. Piston-rod packing should 
always be kept in a clean place, as any dust or 
grit that may become attached to it has a tendency 
to cut or flute the rod. 

Q. What precautions should be taken with the 
piston ? 

A. The spring packing in the cylinder should 
always be kept up to its proper place, because if 
allowed to become loose, the leakage materially 
reduces the power of the engine. Setting out 
packing- rings requires the exercise of great care, 
because, if set too tightly, the friction produced 
will not only have a tendency to cut the cylin- 
der, but will also perceptibly lessen the power 



218 roper's catechism for 

of the engine. The piston should be removed 
from the cylinder at least twice a year, and the 
joints formed by the rings on the flange of the 
head and the follower-plate carefully ground with 
emery and oil. If badly corroded, they should 
be faced up in a lathe and made perfectly steam- 
tight. 

Q. How should the spindle of a ball governor 
be packed ? 

A. Great care should be taken, when packing 
the spindle of a governor, not to screw the pack- 
ing down too tightly, as that would interfere with 
the free movement of the governor. All the parts 
of the governor should be kept perfectly clean and 
free from the gum formed by the use of inferior 
qualities of lubricating oils. 

Q. How should the engine be lubricated ? 

A. All the surfaces subjected to friction should 
be provided with sight-feed oil-cups. These 
should be turned on as soon as the engine is 
started and examined at frequent intervals, to see 
that the supply is not exhausted and to make sure 
that every cup is feeding correctly. 

Q. Is it advisable to use as much oil as possible 
on an engine? 

A. No more oil should be used on an engine 
than is absolutely necessary, as it is not only a 
loss, but often detracts from the appearance of the 



STEAM ENGINEERS AND ELECTRICIANS. 219 

engine, and greatly interferes with its free and eas}" 
movement, from the accumulation of gum and 
dirt on its working parts. 

Q. Suppose any part of the engine should heat, 
what would be the proper thing to do ? 

A. First examine the lubricator, and if it is 
found that the heated part has not been receiving 
the proper amount of oil, the trouble can usually 
be remedied by giving it a liberal supply. Some- 
times it is necessary in a new engine to keep the 
bearings cool, temporarily, with ice, although if 
they run very hot it is generally better to stop 
the engine if possible and determine the cause. 
In case the crank-pin should heat — which is a 
common occurrence with engines having a narrow 
bearing on the pin, but more particularly with 
engines that are slightly out of line — remove the 
key and slacken the strap and box; then pour in 
some flour of sulphur with a liberal supply of 
oil; then adjust the key, and the trouble will 
generally disappear. If the pillow-blocks of an 
engine should heat badly, remove the cap and 
pour in a good supply of pulverized bath-brick 
and water while the engine is in motion; after 
doing this for some time, wash out with oil, and 
wipe the bearing clean with waste. In case any 
of the bearings of an engine should heat through 
the accumulation of matter deposited from the oil 



220 roper's catechism for 

used, or sand, grit, or whitewash being dropped 
into the bearings, use a strong solution of concen- 
trated lye with oil when the engine is in motion. 

Q. Where should the tools and materials used 
about an engine be kept ? 

A, They should be kept in a clean place. 
Never set steam-packing, cotton-waste, tops of 
oil-cups, or anything that is to be used around the 
cylinder, valves, piston-rod, or bearings of steam 
engines, on the floor, as they will invariably pick 
up sand or grit, which injure the rubbing and 
revolving surfaces with which they come in con- 
tact. 

Q. How should gum- joints be made? 

A. If they frequently need to be taken apart, 
the gum should be well coated with pulverized 
chalk or soapstone before being placed between 
the flanges. This prevents it from adhering to 
the metal and being destroyed when the joint is 
broken. 

Q. What does a clicking noise in the cylinder 
indicate ? 

A, It frequently indicates the pressure of moist- 
ure, and it can generally be stopped b}^ opening 
the drip-cocks. 

Q. What are some of the principal causes of 
knocking in steam engines and the appropriate 
remedies ? 



STEAM ENGINEERS AND ELECTRICIANS. 221 

A. Knocking in engines generally arises from 
the following causes: 

First. Lost motion in the boxes on the cross- 
head, crank-pin, and the pillow-blocks, and in 
the key of the piston-rod in the cross-head. To 
stop it, take up lost motion by means of the key, 
or file off the edges of the boxes, if brass-bound. 

Second. It is sometimes caused by the crank 
being ahead of the steam, which in most cases can 
be relieved by moving the eccentric forward in 
order to give more lead an the valve. 

Third. Knocking is caused in many cases by 
too much lead on the valve. The simplest remedy 
for this is to move the eccentric back so as to give 
less lead. 

Fourth. Frequently it is caused by the exhaust 
closing too soon. The best remedy for this would 
be to enlarge the exhaust-chamber in the valve. 

Fifth. Insufficient clearance between the piston 
and the cylinder-head at the end of the stroke. 
The remedy for this kind of knocking would be 
to turn off the heads of the cylinder on the inside, 
so as to give more clearance. 

Sixth. Knocking sometimes arises from the 
wrist of the cross-head and the crank-pin becom- 
ing worn out of round. The most effective remedy 
for this cause is to turn up the crank- and wrist- 
pin. 



222 roper's catechism for 

Seventh. Insufficient counter-bore in cylinder. 
In such cases the piston-rings wear a shoulder at 
each end of the cylinder, and whenever the keys 
are driven or the packing-rings set out, the edges 
strike these shoulders and cause the engine to 
knock. The most practical remedy for knocking 
arising from this cause is to recoimter-hore the 
cylinder. 

Eighth. Knocking is sometimes caused by the 
engine being out of line. The surest remedy for 
this kind of knocking would be to put the engine 
exactly in line. 

Ninth. Sometimes it arises from shoulders be- 
coming worn on the ends of the guides in cases 
where the gibs on the cross-head do not run over. 
The most reliable remedy for such knocking would 
be to replane the guides. 

Tenth. Knocking is sometimes caused by the 
follower-plate being loose. The best preventive 
for such knocking is to bring the bolts up tight. 
To do so, it is sometimes necessary to remove the 
deposit of rust or grease in the bottom of the holes. 

Eleventh. Very often it is caused by the pack- 
ing around the piston-rod being too hard and 
tight. The most effectual remedy for that is to 
remove all the old packing from the box and 
replace it with new, and only screw the box up 
sufficiently to prevent the escape of steam. Too 



STEAM ENGINEERS AND ELECTRICIANS. 223 

much friction on the rod is a great loss of power, 
and has a tendency to destroy the packing. 

Twelfth. The knocking heard in the steam-chest 
is sometimes caused by lost motion in the jam- 
nuts or yoke that forms the attachment between 
the valve and rod. The remedy for this would 
be to remove the cover of the steam-chest and re- 
adjust the jam-nuts on the valve-rod. 



224 roper's catechism for 



ADJUNCTS OF THE STEAM ENGINE. 

THE INDICATOR. 

Q. What do you understand by the steam engine 
indicator ? 

A. An instrument which records the pressure 
in the steam cylinder at every point of the stroke. 

Q. Give a brief description of the instrument 
and explain how this record is made. 

A. The indicator consists essentially of a small 
hollow cylinder which communicates with the 
engine cylinder. A rod attached to the piston is 
enclosed in a spiral spring which presses against 
the piston and opposes its motion. The end of 
the rod extends through the cover at the top of 
the cylinder, and is attached to a series of levers, 
called a parallel motion^ in such a way that a 
pencil attached to the end of the long lever will 
move in a vertical straight line when the piston 
ascends. A second hollow cylinder, carried on 
the same frame as the first, and called the paper 
drum, is mounted on a vertical spindle, about 
which it is free to rotate, but by the action of a 
spring contained in it the drum tends to remain 
in a fixed position. A groove, shown at the bot- 
tom of the drum, carries a cord which is attached 



STEAM ENGINEERS AND ELECTRICIANS.. 



225 



by means of a reducing motion to some of the 
reciprocating parts of the engine, so that the 
pencil, when the engine is moving, would trace a 
horizontal line on the surface of the drum, which 
would represent the stroke of the engine. As the 




SECTION OF TABOR'S INDICATOR. 



pencil, however, is moved up and down by the 
pressure of the steam in the cylinder, it follows 
that, if a paper is placed around the drum, a 
diagram will be traced, representing the pressure 

15 



226 ^ roper's catechism for 

in the cylinder at every point in the stroke. The 
vertical height of any point in the diagram, from 
the bottom or atmospheric line, will represent the 
pressure, and the horizontal distances will repre- 
sent the position of the piston. 

Q. How would you proceed to take an indicator 
diagram ? 

A. It is impossible to give directions which 
would apply to all makes of indicators. I should 
carefully read the directions given by the makers 
of the particular type of instrument in my pos- 
session, and proceed accordingly. 

Q. Sketch an indicator diagram and explain 
what it means. 

A. In the accompanying diagram the line A A 
is the atmospheric line — that is, it is the line 
traced by the pencil on the paper when the engine 
is in motion before the indicator cylinder is placed 
in communication with the engine cylinder. 
Hence its position represents the pressure of the 
atmosphere. The point B represents the position 
of the pencil at the beginning of the stroke, and 
hence the vertical height B A of this point above 
the atmospheric line A A represents the initial 
steam pressure in the cjdinder. The line B C 
represents the distance traveled by the piston 
during the period of admission, and the point C, 
where the first change in direction occurs, is the 



STEAM ENGINEERS AND ELECTRICIANS. 



227 



point of cut-off. Expansion now takes place in 
the cylinder and continues until the next change 
in direction occurs at D, which is the point at 
which the exhaust port begins to open. The 
steam is released from the cylinder, and the pres- 
sure falls more rapidly until the end of the stroke 
E, when it is about equal to that of the atmos- 



HHhI 



EXPLANATORY DIAGRAM. 



phere. The piston then begins its return stroke 
against the back pressure represented by the ver- 
tical height of the line E F above the atmospheric 
line A A. If the engine exhausts into the atmos- 
phere, this height is generally very small, while 
if it is a condensing engine, the back pressure 
line E F will be below the atmospheric line A A, 



228 roper's catechism for 

indicating a negative back pressure. At F the 
exhaust closes and compression begins, which 
continues until the end of the stroke G. The 
same cycle is then repeated, and so long as the 
load, the initial pressure and the back pressure 
remain the same, the diagram traced by each 
successive stroke will be practically the same. 
For the other end of the cylinder the diagram 
will be similar but reversed. 

Q. What are the principal things that may be 
ascertained about an engine with the aid of the 
indicator diagram ? 

A. The information furnished by the indicator 
diagram is of the most important kind. It en- 
ables us to determine: 

First. The power of the steam engine under all 
conditions, or the power consumed by any one 
machine driven by the engine or by the engine 
itself in overcoming the friction of its parts. 

Secondly. The forward and back pressure on 
the piston at any point in the stroke. 

Thirdly. The average forward and back pres- 
sure and the mean effective pressure on the piston. 

Fourthly. The positions of the piston when 
steam is admitted and cut off; the period of ex- 
pansion, exhaust, and compression; the action of 
the valves; and, in fact, all questions relating to 
the steam distribution. 



STEAM ENGINEERS AND ELECTRICIANS. 229 

Q. How is the power developed by the engine, 
or the indicated horse-power calculated from the 
diagram ? 

A. The indicated horse-power of the engine is 
fomid by determining the mean effective pressure 
from the diagram and using it in the rules and 
formulae for horse-power given on pages 177-180. 

Q. Explain how to find the mean effective 
pressure. 

A. There are two methods in common use, — 
one by the use of ordinates and the other by the 
planimeter. The latter method is more exact and 
less laborious than the former, but as a plan- 
imeter is not always available, the former method 
is much used, especially for rough calculations. 

TO DETERMINE THE MEAN EFFECTIVE 
PRESSURE. 

First Method. — Draw vertical lines A B and A I 
touching the ends of the diagram (see page 227), 
and apply a rule across them obliquely as shown 
by the dotted line in the diagram in such a way 
that some division on the rule, as y^g-, ^, ^, or ^, 
will divide the distance between the verticals just 
drawn an even number of times, preferably 20 
times. Mark off points on this line, dividing it 
into equal parts excepting the first and last, which 
are only one-half as large as the intermediate 



230 roper's catechism for 

spaces, and draw vertical lines or ordinates 
through these points, dividing the area enclosed 
by the diagram as shown. Next take a long strip 
of paper and apply its edge successively to each of 
the ordinates and mark their combined length on 
it. This length multiplied by the scale of the 
spring used and divided by the total number of 
ordinates will give the mean effective pressure. 
The length of the ordinates is measured between 
the forward- and back-pressure lines. 

Second Method. — If a planimeter is used, it is 
only necessary to multiply the area enclosed by 
the diagram in square inches by the scale of the 
spring, and divide the product by the length of 
the diagram in inches. The quotient will be the 
mean effective pressure. 

Q. What precautions must be taken if the indi- 
cated horse-power is to be calculated very accu- 
rately ? 

A. The mean effective pressure must be calcu- 
lated separately from the diagrams of the head- 
and crank-ends of the cylinder. In doing this it 
must be remembered that the back-pressure line 
of one diagram belongs to the forward-pressure 
line of the other, and vice versa. While in most 
engines in which the valves are properly adjusted 
the two back-pressure lines are identical, yet if 
the greatest accuracy is desired the mean effective 



STEAM ENGINEERS AND ELECTRICIANS. 231 

pressure should be calculated by deducting from 
the mean forward pressure as obtained from the 
head-end diagram, the mean back pressure as 
obtained from the crank-end diagram, and vice 
versa. It must further be borne in mind that the 
effective area of the piston at the crank end is less 
than that at the head end by the area of the piston 
rod. Hence the horse-power is different for the 
two ends and should be calculated independently; 
the total horse-power of the engine being equal to 
the sum of the two. 

Q. Suppose it is desired to find the horse-power 
of an engine where the following dimensions and 
data are known: 

Stroke = 36 inches. 
Diameter of cylinder = 24 inches, 
Speed = 150 revolutions per minute, 
Diameter of piston rod = 4 inches. 

The engine having been indicated with a spring 
whose scale was 60 pounds per square inch, it was 
found with the aid of a planimeter that the areas 
of the diagrams w^ere as follow^s: 

Head end = 3. 54 square inches, 
Crank end = 3.42 square inches, 
Length of diagrams = 3.27 inches. 

Calculate the mean effective pressures and the 
horse-power of the engine. 



232 roper's catechism for 

A. The mean effective pressure, according to the 
above (second) method, is — 

Head end, ^ ^„ — ^ 64.95 pomids, 

Crank end, ^ „ = 62. 32 pomids. 

The area of the piston is — 

.7854 X 24 X 24 = 452.39 square inches, 
and the area of the piston rod is — 

.7854 X 4 X 4 = 12.57 square inches. 
Hence the effective areas of the piston are — 
Head end, 452.39 square inches. 
12.57 " 



Crank end, 439.82 " 

The total mean pressures on the piston are — 

Head end, 452.39 X 64.95 = 29385 pounds, 

Crank end, 439.82 X 62.32 = 27409 pounds. 

The piston speed is — 

36 

12 

and therefore the horse-power — 

jr A A 29385 X 900 „^, . 
Headend.— 33^^^— ^801.4 

^ , T 27409 X 900 
Crank end, 33000 ^ 



Total, 1548.9 



STEAM ENGINEERS AND ELECTRICIANS. 233 

CONDENSERS. 

Q. What do you understand by a condenser ? 

A. An apparatus for condensing the exhaust 
-steam of an engine, thereby reducing the back 
pressure and therefore increasing the power. 

Q. How is this done ? 

A. By bringing the steam under the influence 
of cold water, either by bringing the two in direct 
contact or by allowing the steam to pass around a 
series of tubes through which the w^ater flows. 
Condensers constructed on the first-named plan 
are called jet condensers^ while the latter are termed 
surface condensers. 

Q. What are the principal advantages and dis- 
advantages of the two types ? 

A. Surface condensers have the advantage that 
the condensed steam is not mixed with the con- 
densing water. Hence they are generally used on 
shipboard so that the condensed steam may again 
be used in the boilers. The vacuum is also 
generally higher in surface than in jet condensers, 
but they have the disadvantage of being heavier 
and much more expensive to construct than jet 
condensers. The tubes are also liable to become 
leaky and impair the vacuum. 

Q. At what temperature should jet condensers 
be kept? 



234 roper's catechism for 

A. About 100° Fahr., at which temperature 
they have been found to operate most efficiently. 

Q. What degree of vacuum should exist in a 
good condenser ? 

A. From 20 to 26 inches. 

Q. What do you mean by 26 inches of vacuum ? 

A. As the atmospheric pressure will support a 
column of mercury about 30 inches in height, 
each inch of the mercury column would be equiv- 
alent to a pressure of about ^ pound. A complete 
vacuum (which can never exist) would be a 
vacuum of 30 inches, corresponding to a pressure 
of pound per square inch; 20 inches of vacuum 
would be one-third less vacuum or one-third of 
the atmospheric pressure — that is, 5 pounds per 
square inch absolute pressure. Hence to find the 
absolute pressure in pounds per square inch, 
deduct one-half of the vacuum in inches from the 
pressure of the atmosphere. Thus 15 inches of 
vacuum would be, 15 — 15 X i = 7J- pounds 
per square inch absolutely. 

Q. How much power is gained by the use of 
the condenser? 

A. From 20 to 30 per cent., depending on the 
type and size of the engine. 

Q. How much water is required for condensers ? 

A. About 25 times the quantity evaporated in 
the boiler. 



STEAM ENGINEERS AND ELECTRICIANS. 



235 



TABLE 

SHOWING VACUUM IN INCHES OF MERCURY AND POUNDS 
PRESSURE PER SQUARE INCH. 



Mercury. 


Founds, 


Mercury. 


Pounds. 


2.037 


1 


16.300 


8 


4.074 


2 


18.337 


9 


6.111 


3 


20.374 


10 


8.148 


4 


22.411 


11 


10.189 


5 


24.448 


12 


12 226 


6 


26.485 


13 


14.263 


7 


28.552 


14 



236 eoper's catechism for 



MATERIALS AND THEIR PROPERTIES. 

Q. Of what is all matter made up ? 

A. Of chemical elements. 

Q. What are chemical elements ? 

A. Substances having certain definite and pecu- 
liar properties which, so far, chemists have not 
been able to split up into simpler substances, and 
which it is presumed cannot be further split up. 

Q. What are some of the elements ? 

A. Among the metals : Iron, Copper, Lead, Tin, 
Zinc, Silver, Gold, and Platinum. Among the 
non-metals are: Antimony, Bismuth, Silicon, Sul- 
phur, and Carbon. Among those which exist nor- 
mally in the gaseous condition are: Hydrogen, 
Oxygen, Nitrogen, and Chlorine. 

Q. What are the substances called which are 
made up by the chemical combination of two or 
more elements? 

A. Compounds, as, for example, Water, which 
is a compound of Oxygen and Hydrogen; Ammo- 
nia, which is a compound of Nitrogen and Hydro- 
gen; Carbonic Acid, which is a compound of Car- 
bon and Oxygen; Zinc Oxide, which is a compound 
of Zinc and Oxygen; and common Salt, which is 
a compound of Sodium and Chlorine. 



STEAM ENGINEERS AND ELECTRICIANS. 237 

Q. What are the molecules of a substance ? 

A. The smallest particles mto which a substance 
can be divided without these particles losing any 
of the distinctive properties of the substance. 

Q. Have you any idea as to whether molecules 
are visible under the microscope ? 

A. They are not. Were the magnifying power 
in any way much increased, they would still be 
too small to be seen. Our ideas as to their exist- 
ence are derived not from sight, but from a variety 
of chemical phenomena. 

Q. Is it conceived that there are particles even 
smaller than molecules ? 

A. Yes, the so-called atoms. It is believed that 
each molecule of a compound substance is made 
up of the atoms of the elements contained in the 
compound. For example, the molecule of salt is 
supposed to be made up of an atom of sodium 
joined to an atom of chlorine, and the water mol- 
ecule is supposed to be made up of two hydrogen 
atoms joined to one oxygen atom. The molecules 
of the elements are supposed to be made up of 
two or more atoms of that element. 

Q. What is meant by the term ' ' atomic weight ' ' 
of a substance ? 

A. It is found experimentally that the elements 
combine with each other in certain fixed propor- 
tions or in multiples of them. The figures which 



238 roper's catechism for 

represent these proportions (hydrogen bemg used 
as the standard and its combining weight called 
"one") are called the atomic weights. For ex- 
ample: Experiment shows that hydrochloric acid 
is made up of 35.4 parts b}^ weight of chlorine to 
1 part by weight of hydrogen; and that in other 
chlorine compounds the proportion of chlorine is 
represented either by 35.4 or by some multiple of 
it, as 35.4 X 2, 35.4 X 3, etc. Thus, salt is made 
up of 35.4 parts by weight of chlorine to 23 parts 
by weight of sodium. 

Q. What is supposed as to the construction of 
substances according to the molecular theory ? 

A. Every substance is supposed to be made up 
of an immense number of molecules, which, even 
in the solid state, are never entirely at rest, and 
in the gaseous state are in perpetual violent com- 
motion, rushing about in straight lines in all di- 
rections with enormous rapidity. 

Q. What are the principal properties of metals ? 

A. Their malleability, or capability to stand ham- 
mering; their ductility, or power of being drawn 
out into wire; their tenacity, or strength; their 
hardness ; their fusibility, or ease of melting; and 
their relative weight, or specific gravity. 

Q. Name some of the most malleable of the 
common metals. 

A. Gold, Silver, Aluminum, Copper, Tin, Lead. 



STEAM ENGINEERS AND ELECTRICIANS. 239 

Q. Name the most ductile. 

A. Platinum, Silver, Iron, Copper, Gold. 

Q. What are some of the strongest ? 

A. Iron, Copper, Aluminum, Platinum, Silver. 

Q. What are some of the least fusible ? 

A. Platinum, Iron, Copper. 

Q. AVhat are some of the heaviest, or which 
have the greatest specific gravity ? 

A. Platinum, Gold, Lead, Copper, Iron. 

Q. How would you define the specific gravity 
of a substance ? 

A, The ratio of its weight to the weight of an 
equal bulk of water. 

Q. How would you find the specific gravity of 
a solid body ? 

A. If it is heavier than water, weigh it in air 
and then weigh it suspended in water. The dif- 
ference in weight is the weight of an equal bulk 
of water. Divide the weight in air by the weight 
of the equal bulk of water and the quotient is the 
specific gravity. 

If the body floats put just the weight oil it that 
is necessary to make it sink even with the surface 
of the water. Then from the sum of this weight 
and the weight in air subtract the weight in water. 
The difference is the weight of an equal bulk of 
water. Divide the weight in air by this and the 
quotient will be the specific gravity. 



240 eoper's catechism for 

Q. How would you measure the specific gravity 
of a liquid ? 

A. Take a vessel filled with it and weigh it. 
Then weigh the same vessel filled with water. 
Divide the weight of the substance by the weight 
of the water and the quotient will be the specific 
gravity. 

Q. Is there any simple instrument for testing 
the specific gravity of liquids ? 

A. Yes; the hydrometer, which consists of a 
graduated tube of small diameter attached to a 
bulb containing air enough to make it float. Just 
below this air chamber is a small bulb containing 
enough mercury to keep the apparatus upright. 
The graduations on the tube give the specific grav- 
ity of the liquid in which the hydrometer is placed. 

Q. Is water used as the standard of specific 
gravity for gases ? 

A. No; air at a standard temperature of 32° 
Fahr. and at a pressure corresponding to the at- 
mosphere at sea level. 

COMMON METALS. \ 

Q. What are the varieties of iron ? 
A. Wrought iron, cast iron, and malleable iron. 
Q. What is steel? 

A. A modification of iron, it being a combina- 
tion of iron with varying percentages of carbon. 



STEAM ENGINEERS AND ELECTRICIANS. 241 

Q. What are some of the properties of wrought 
iron? 

A. It is tough, malleable, ductile, fibrous, and 
can be welded. 

Q. How does cast iron differ from wrought 
iron ? 

A. It contains carbon, sulphur, silicon, phos- 
phorous and other impurities. It is crystalline 
in structure, is neither malleable, ductile, nor 
tenacious, but has the very important property of 
allowing itself to be cast. 

Q. What is malleable iron ? 

A. Cast iron annealed amid iron oxides. 

Q. What are its properties ? 

A. It is much more ductile than cast iron and 
has a higher tensile strength, though far inferior 
in both respects to wrought iron and steel. 

Q. What are the properties of steel ? 

A. Steel partakes of the properties of both 
wrought and cast iron, as some steels can be cast 
and others welded. By varying the percentage of 
carbon in its composition its characteristics can be 
widely changed. It can be made soft and ductile 
or hard and brittle. Steel also has the important 
property of teinpermg, or being artificially hard- 
ened by sudden changes of temperature. 

Q. What effect on the strength of steel does an 
increase of the percentage of carbon have ? 
16 



242 roper's catechism for 

A. It increases the strength of steel. 

Q. What effect does it have on the ductihty of 
steel? 

A. The ductility is diminished. 

Q. At about what temperature is iron red hot ? 

A. At about 1000° Fahr. 

Q. At about what temperature does iron melt ? 

A. At about 3000° Fahr. 

Q. How much is iron expanded when its tem- 
perature is raised from freezing point to boiling 
point ? 

A. About -glo of its length. 

Q. AVhat is the effect of a rise of temperature 
on the strength of iron ? 

A. It increases nearly -^ to about 600° Fahr., 
after which it falls. At 1000° Fahr. its strength 
is about half the maximum. 

Q. How does copper compare with iron in its 
principal qualities? 

A. It is more malleable and more ductile. Its 
tensile strength is a little less than one-half. Its 
specific gravity is a little greater. It is a much 
better conductor for heat and electricity, its elec- ^ 
trical conductivity being about six times that of 
iron. 

Q. How is the tensile strength affected by heat ? 

A. It is diminished, disappearing entirely at 
about 1300° Fahr. 



STEAM ENGINEERS AND ELECTRICIANS. 243 

Q. What is the temperature at which copper 
melts? 

A. At about 2000° Fahr. 

Q. In what form is copper mostly used ? 

A. In the form of sheets and wires. 

Q. In what other ways is it largely used ? 

A. In combination with other metals forming 
alloys. 

Q. What are some of the principal alloys ? 

A. Brass, Bronze, and German Silver. 

Q. What is the composition of brass ? 

A. It varies with the purpose for which it is to 
be used. Ordinary brass in foundries consists of 
2 parts copper to 1 part zinc. A little tin or lead 
is sometimes added, but essentially brass is an 
alloy of copper and zinc. 

Q. What is bronze ? 

A. Bronze is essentially an alloy of copper and 
tin, consisting of about 8 parts copper to 1 part 
tin. 

Q. What is German Silver ? 

A. An alloy of copper and zinc, having a com- 
position of about 3 parts copper to 1 part zinc. 

Q. What are some of the striking properties of 
lead? 

A. Its softness and malleability and its lack of 
elasticity. A very valuable property is that it is 
not readily oxidized nor attacked by acids. 



244 roper's catechism for 

Q. For what purposes is it largely used ? 

A. In sheets, pans, and pipes and as a constit- 
uent of paints. 

Q. How does it compare, in tensile strength, 
with iron ? 

A. Its tensile strength is very small indeed in 
comparison with that of iron. 

Q. What is its melting point? 

A. About 600° Fahr. 

Q. What is its specific gravity ? 

A. About 11, nearly double that of iron. 

STRENGTH OF MATERIALS. 

Q. What do you understand by the breaking 
strength of a substance ? 

A. The force, in pounds per square inch, that 
must be exerted to break a specimen of that sub- 
stance when it is placed in a suitable testing 
machine. The breaking strength may be either 
tensile or compressive. 

Q. What is the tensile strength ? 

A. The number of pounds necessary to pull 
asunder the test piece of 1 square inch cross-sec- 
tion, the force being applied in a line perpendicu- 
lar to the plane of the section. 

Q. What is the compressive strength ? 

A. The number of pounds that must be applied 
to crush the test piece. 



STEAM ENGINEERS AND ELECTRICIANS. 245 

Q. What is the tensile strength of cast iron ? 

A. About 16,000 pounds per square inch. 

Q. What is the compressive or crushing 
strength ? 

A. About 100,000 pounds. 

Q. What are the tensile and compressive 
strengths of wrought iron ? 

A. They are about the same, viz. , 50, 000 pounds. 

Q. What can you say of the strength of steel ? 

A. It may be made to have almost any value, by 
varying the composition, from 50,000 to 200,000 
pounds per square inch. The great increase in 
strength is accompanied by brittleness. 

Q. What are the strengths of oak and pine ? 

A. Tensile about 7000 pounds and compressive 
about 3500 pounds per square inch. 

Q. In calculating the sizes of pieces, either 
metal or wood, are the above figures used without 
any allowance for uncertainties? 

A. No; we make use of what is termed a Factor 
of Safety. We assume that the load coming on 
the piece is a certain number of times greater 
than it really is and calculate the size of the piece 
accordingly. The ratio between the assumed load 
and the real load is the Factor of Safety. 

Q. What values are used for the factor of 
safety ? 

A. This depends entirely upon the nature of 



246 roper's catechism for 

the load. If it is steady, with no vibration as in 
the roofs of houses, the factor is taken as three. 
When the load is fairly nniform, but with vibration, 
as in the case of shafting hung from the roof trusses, 
the factor should he four. If the direction of the 
load is reversed, putting the piece in alternate ten- 
sion and compression, the factor should be six. 

Q. Suppose it were desired to hang a weight of 
50,000 pounds on the lower end of a wrought-iron 
rod. What should be the area of the cross-section 
of the rod ? 

A. This is a case of a steady load where the 
factor of safety to be used is three. Multiplying 
the actual load by 3 we obtain 150,000 pounds as 
the load to be assumed. The tensile strength of 
wrought iron being about 50,000 pounds per 
square inch, it is evident that we must have a 
section of 150,000 ^- 50,000, or 3 square inches. 

Q. On what does the weight that a beam will 
support, depend? 

A. On the length of the beam between the 
points of support, on its width and depth, and 
on the manner of application of the load. 

Q. What difference does it make as to the 
manner of loading the beam ? 

A. It will support a much greater load if it is 
uniformly loaded than if the load is applied at 
one point. 



STEAM ENGINEERS AND ELECTRICIANS. 247 

Q. What do you mean by a uniformly loaded 
beam ? 

A. A beam is uniformly loaded when the weight 
per square inch resting on it is the same at all 
parts of its length. 

Q. When a beam is supported at both ends, at 
what point will a given load break the beam most 
readily ? 

A. At the middle of the beam. 

Q. What is the difference between the load 
which if applied in the middle will break a beam, 
and the load needed to break it if it is uniformly 
distributed ? 

A. A given beam will support a uniformly 
distributed load twice as great as that which will 
break it if it is applied at the middle. 

Q. Can the values for crushing strength be safely 
used in all cases ? 

A. Not when the length of the piece in com- 
pression has a length greater than four times a 
diameter. When this is the case the piece 
becomes a column, and a bending action comes 
into play, causing the piece to break long before 
the load corresponding to the compressive strength 
has been reached. 



248 roper's catechism for 



ELECTRICITY* 

Seven simple experiments contain the funda- 
mental principles on which nearly all electrical 
apparatus depends. 

Experiment 1. — Place in a jar containing a solu- 
tion of chromic acid a plate of zinc and a plate 
of carbon. The plates should be near each other 
without actually touching, and each should have 
fastened securely to it a short piece of small 
copper wire. Place in another glass jar a solution 
of copper sulphate and let the ends of the copper 
wires dip into the copper sulphate solution with- 
out touching each other. 

Q. AVhat will happen to that part of the copper 
wires dipping into the solution ? 

A. The wire attached to the carbon plate will 
be gradually eaten away, while the wire attached 
to the zinc plate will increase in size by an equal 
amount. 

Q. AVhat is deposited on this wire to increase 
its size ? 

A. Pure copper. 

Q. Suppose this wire were made of some other 
material than copper, would copper be deposited 
on it? 

A. Yes; if made of iron, zinc, lead, or carbon. 



STEAM ENGINEERS AND ELECTRICIANS. 249 

Q. What does this experiment seem to show ? 

A. That there has been set up a current of 
something which apparently carries copper along 
with it. 

Q. What name has been given to this current ? 

A. The electric current. 

Q. Could other plates than zinc and carbon be 
used to jjroduce it ? 

A. Yes; though zinc is generally used for one 
of the plates. 

Q. Could another solution than chromic acid 
be used ? 

A. Yes; the solution must be one which readily 
attacks one of the plates, and it is usually some 
strong acid. 

Q. What is the apparatus called in which an 
electric current is produced by chemical action ? 

A. A battery cell, or, simply, a cell. 

Q. What is a battery ? 

A. Properly speaking, a battery means several 
cells, but it is often used to mean simply one 
cell. 

Q. What is the wire called to which copper is 
carried ? 

A. The kathode. 

Q. What is the wire called from which copper 
is taken ? 

A. The anode. 



250 eoper's catechism for 

Q. In which direction does the current flow in ; 
the copper sulphate solution ? ; 

A. From the anode to the kathode. 

Q. Is there a current flow through the cell con- 
taining chromic acid ? 

A. Yes; resulting in taking zinc from the zinc 
plate and carrying it into solution. 

Q. Suppose one of the copper wires were cut, 
what effect would this have on the flow of current ? 

A. It would stop completely the action described 
above. 

Q. What does this show ? 

A. That what is called the electric current was 
flowing around through a path or circuit, starting, 
say, at the carbon plate, thence through the copper 
Avire attached to that plate to and through the 
solution of copper sulphate, then through the 
other wire to the zinc plate, and finally through 
the chromic acid solution back to the carbon 
plate. Any interruption of this circuit stops the 
flow of current. 

Q. Would pulling one of the wires out of the 
copper sulphate solution have the same effect as 
cutting the wire ? 

A. Yes. 

Q. Of what electrical industry is this experi- 
ment the basis ? 

A. Electro-plating. 



STEAM ENGINEERS AND ELECTRICIANS. 251 

Experiment 2. — Pull the copper wires out of the 
copper sulphate solution and touch them together. 

Q. What will be observed ? 

A. The wires become heated. 

Q. Equally all along their length ? 

A. Apparently so. 

Q. Is the zinc plate being dissolved as in Ex- 
periment 1 ? 

A. Yes. 

Q. What does this experiment show ? 

A. That the electric current heats bodies through 
which it passes. 

Q. Suppose the wire connecting the zinc and 
carbon plates is made longer, what will occur ? 

A. The heating will be less. 

Q. And if the wire is made shorter ? 

A. The heating effect is much greater. 

Q. What would you infer from this ? 

A. Since a decrease in the heating means a 
decrease in the current, and since this was caused 
by lengthening the wire, it would seem that the 
wire opposes a resistance to the flow of the elec- 
tric current, and that the longer the wire the 
greater the resistance which it offers. 

Q. Can you think of any electrical apparatus 
working on the principle shown in this experiment ? 

A. Electric heaters and certain electric measur- 
ing-instruments. 



252 roper's catechism for 

Experiment 3. — Bring a compass needle or a 
freely suspended bar magnet near the wire in Ex- 
periment 2. 

Q. What will be observed ? 

A. The magnet is evidently acted upon by some 
force due to the current flowing through the wire. 
After oscillating it comes to rest, pointing cross- 
ways to the wire and nearly perpendicular to it. 

Q. Is this the case all along the wire ? 

A. Yes. 

Q. Why does the needle not stand exactly per- 
pendicular to the wire ? 

A. Because normally it tends to point north. 
The current through the wire tends to make it 
stand perpendicular to the wire. It actually takes 
a direction between these two. 

Q. Notice which way the north-seeking pole of 
the magnet points. Now, if the magnet is held 
first above the wire and then below, what occurs ? 

A. Although the needle tends to stand in a 
direction cross- ways to the length of the wire, yet 
when above the wire the north-seeking pole points 
in one direction, and when below the wire in the 
opposite direction. 

Q. Is there any rule for telling in what direction 
it will point? 

A. Yes, one known as Ampere's rule, which is: 
^'Imagine yourself swimming with the current and 



STEAM ENGINEERS AND ELECTRICIANS. Zo6 

turned either on your side, face, or hack, so as to look 
at the magnet. Then the north-seeking pole of the 
magnet luill point toivard your left. ' ' 

Q. In the above experiment, suppose that the 
wire carrying the current is free to move while 
the magnet is fixed, what will occur ? 

A. The Avire will move either toward or away 
from the magnet, according as one pole or the 
other of the magnet is presented to it. 

Q. What does this show? 

A. That there is a force existing between a 
magnet and a wire carrying a current, similar to 
the force existing between two magnets. Further 
experiment shows that the strength of this force 
depends on the nearness of the magnet to the wire 
carrying current, and that the direction of the force 
depends on the position of the wire with respect 
to the two poles of the magnet. 

Q. Can this magnetic force be represented con- 
veniently by lines as in the case of other forces ? 

A. Yes. We conceive that around every mag- 
net or wire carrying current lines could be drawn 
either straight or curved, which at any point of 
their length should represent the direction of the 
resultant magnetic force at that point. 

Q. How could you actually lay out the lines of 
force due to any magnet, say a bar magnet ? 

A. If we could obtain a north-seeking pole of a 



254 roper's catechism for 

magnet without its accompanying south-seeking 
pole, we could place it near the north-seeking pole 
of the bar magnet and observe the path which it 
pursued from the north pole to the south pole and 
plot this path on paper. We would then place 
the test pole at another point of the north pole of 
the bar magnet, and again observe the path and 
plot it, and so on. In this way the space around 
the magnet could be mapped out. 

Q. What is the space around a magnet, in 
which magnetic force exists, called? 

A. The field of that magnet. 

Q. Does every magnet have a field ? 

A. Yes; and since lines of force could be drawn 
in this field which would represent the direction 
of magnetic force, we say that every magnet pro- 
duces lines of force. 

Q. What, then, is a line of force ? 

A. It is a line which represents the direction of 
magnetic force in the region where the line is 
drawn or may be supposed to be drawn. 

Q. What is the positive direction of the line of 
force ? 

A. That direction in which a free north-seeking 
magnetic pole would move. A free south pole 
would move in the opposite direction. 

Q. Since we cannot obtain a free north pole for 
testing the direction of magnetic force, how can 



STEAM ENGINEERS AND ELECTRICIANS. 255 

we explore and map out the magnetic field due to 
any magnet or wire carrying current ? 

A. By taking advantage of the fact that a short 
magnet will, if free to move, place itself length- 
wise along the lines of force. 

Q. Explain how the experiment is performed. 

A. Place under a piece of window-glass a bar 
magnet, and dust on the 
upper side of the glass 
some iron filings. These 
filings become magnets 
which are exceedingly 
short, and when they are 
jarred by tapping the glass 
they are free to move 
and set themselves into 
lines corresponding to the 
lines of magnetic force as shown in the cut. 

Q. Why are the lines of filings more dense at 
some points of the field than at others ? 

A. Because the strength of the magnetic force 
is greater at those portions of the field. 

Q. How would you describe the lines of force 
due to a bar magnet ? 

A. As curved lines running from the north pole 
to the south pole. 

Q. What are the lines of force due to a horse- 
shoe magnet ? 




256 



roper's catechism for 



A. Principally straight lines from the north to 
the south pole. 

Q. How can you obtain the field due to a cur- 
rent in a straight wire ? 

A. By drilling a hole in the piece of glass and 
passing the wire vertically through this hole and 
then dusting on iron filings. 

Q. AVhat are the lines of force due to a current 
in a wire ? 

A. Circles concentric with the axis of the wire, 
the positive direction be- 
ing in the direction in 
which the hands of a 
watch move. 

Q. Where is the mag- 
netic force greatest ? 

A. Next to the wire, as 
shown by the greater den- 
sity of the lines of force. 
Q. Suppose the current 
through the wire were greatly increased, how 
would the density of the lines be affected ? 

A. It would be increased in the same proportion 
as the magnetic effect of the current is strictly 
proportional to the strength of the current. 

Q. When a coil of wire carrying a current is 
brought near a magnet, can the direction of 
motion of the coil or magnet be told in advance ? 




STEAM ENGINEERS AND ELECTRICIANS. 257 

A. Yes; they will move in such a way that the 
greatest possible number of lines of force due to 
the magnet will pass through the coil. 

Q. For what practical purpose can this principle 
of the effect of an electric current on a magnet be 
used ? 

A. AYe can detect currents in wires by bringing 
a magnet near. the wires, and can also, by applying 
Ampere's rule, determine in which direction the 
current flows. 

Q. Is there any other method of determining 
the direction of flow of a current. 

A. Yes; by making use of the principle illus- 
trated in Experiment 1. The current can be led 
into a solution of copper sulphate (or nearly any 
solution of a metallic salt), and by noting which 
of the wires increases in size we can tell in which 
direction the current flows, as it flows toivard the 
wire which has copper deposited on it. 

Q. Can we increase the effect of the current on 
the magnet ? 

A. Yes, in three ways : By increasing the 
strength of current, by bringing the wire and the 
magnet nearer together, and by winding the wire 
which carries the current in a coil and placing the 
magnet in the axis of the coil. 

Q. When this is done, what direction will the cur- 
rent in the coil tend to make the magnet assume ? 
17 



258 roper's catechism for 

A, A direction parallel to the axis of the coil. 
Since the magnet is also acted on by the earth's 
magnetism tending to make it point north, it will 
actually assume a position between these two 
directions. The angle which it makes with north 
depends on the relative strength of the earth's 
magnetic force and the magnetic force due to the 
coil. AVith no current passing through the coil 
the magnet points due north. When a small cur- 
rent passes through the coil the magnet is slightly 
deflected. A larger current deflects it more, and 
so on. 

Q. What is the apparatus called which consists 
of the coil of wire and pivoted magnet described 
above? 

A. A galvanometer. 

Q. For what purposes should you say that the 
galvanometer would be useful ? 

A. For detecting the presence of electric cur- 
rents, determining in which direction they flow 
and also to nxeasure their strength. 

Experiment 4- — Connect to a galvanometer, as 
described above, the terminals of an auxiliary 
coil of wire placed a few feet distant, the connec- 
tion being made by leading a wire from one end 
of the auxiliary coil to one end of the galvanom- 
eter coil, and another wire from the other end of 
the auxiliary coil to the other end of the galvanom- 



STEAM ENGINEERS AND ELECTRICIANS. 259 

eter coil. Bring a strong magnet near the auxil- 
iary coil, watching at the same time the magnet 
needle of the galvanometer. 

Q. What occurs? 

A. The magnet needle gives a sudden jump 
and continues to oscillate to and fro, coming to 
rest a little while after the motion of the strong 
magnet has stopped. 

Q. What does this show ? 

A. The jump of the galvanometer needle shows 
that an electric current has been produced by 
moving the magnet near the auxiliary coil. The 
fact that after the magnet stops the needle comes 
to rest in its original position, shows that the cur- 
rent is produced only while the magnet is moving. 

Q. Suppose that instead of moving the magnet 
toward the auxiliary coil, the coil is moved 
toward the magnet ? 

A. The galvanometer needle jumps in the same 
direction as before, showing that current is pro- 
duced in the same way and in the same direction. 

Q. Suppose that the magnet and coil are moved 
away from each other? 

A. The needle jumps as before, but in the 
opposite direction. 

Q. What do you conclude from all this ? 

A. That moving a wire and a magnet relatively 
to each other produces an electric current, and 



260 



ROPER'S CATECHISM FOR 



that the direction of the current depends on the . 
direction of the motion. ; 

Q. Has the current so produced the same ' 
properties as the current produced by a battery ? 
A. Absolutely the same; the two are identical. 
Q. What piece of electric apparatus is based on 
the principles illustrated by this experiment ? 
A. The dynamo. 

Q. Making use of the idea of lines of force in 
the above experiment, what result do you arrive at ? 
A. Moving the magnet nearer the coil causes 
the coil to cut across lines of force due to the 
magnet, and since a current is produced by the 
motion we may conclude that ivhenever an electric 
conductor cuts across lines of force an electric current 
is produced. 

Q. When the magnet was moved away there 
was a current produced in the opposite direction 
by the cutting of lines of force. Is there any 
convenient rule for de- 
termining the direction 
of the induced current ? 
A. Yes; a rule known 
ion of as Fleming's. 
'"■ Point the forefinger along 

the positive direction of the 
magnetic lines and point 
the thumb stretched at right 




STEAM ENGINEERS AND ELECTRICIANS. 261 

angles in the direction in ichich the conductor moves. 
If now the second finger he stretched at right angles 
to both thumb and forefinger, it will point in the direc- 
tion of the induced current. 

Q, When the magnet is moved nearer the coil, 
the number of Hnes of force due to the magnet, 
which is enclosed by, or which passes through, the 
coil, is increased, might we not say that a cur- 
rent is produced w^henever the number of lines 
enclosed by a coil is changed ? 

A. Yes; and when the conductor is in the form 
of a coil this idea is of great value. Looking along 
the positive direction of the lines of force, when the 
number enclosed by the coil is increased, the cur- 
rent around the coil is left-handed as we look at it. 
If the number enclosed by the coil is diminished, 
the current will be right-handed as we look at it. 

Q. What do you mean by right-handed ? 

A. In the direction in which the hands of a 
watch move. 

Experiment 5. — If the current from a battery or 
other current generator be led through a wire 
Avhich is coiled around a rod of iron, the iron 
becomes strongly magnetized, as we say ; that is, it 
exhibits all the properties of a magnet. It at- 
tracts other pieces of iron, and it has polarity, 
one end attracting the north-seeking pole of a bar 
magnet and the other end repelling it. 



262 roper's catechism for 

Q. What is the combination of a piece of iron 
with a coil of wire around it called ? 

A. An electro-magnet. 

Q. After current is cut off from the coil, does 
the iron still exhibit magnetic qualities ? 

A. Only feebly. The magnetism still remain- 
ing is called permanent or residual magnetism. 

Q. What is the advantage of an electro-magnet 
over a permanent magnet ? 

A. For the same size the electro-magnet is 
much more powerful. 

Experiment 6. — Suspend a coil of wire so that 
it can turn freely and lead a current through the 
wire. Then bring a magnet near it. 

Q. Will the coil be affected by the magnet ? 

A. Yes, the coil will turn so as to enclose as 
many as possible of the lines of force due to the 
magnet and will finally come to rest in that position. 

Q. Suppose the other pole of the magnet be 
presented toward the coil ? 

A. The coil will turn in the opposite direction 
and come to rest in such a position that it encloses 
the greatest possible number of lines of force due 
to the magnet. 

Q. Suppose just at the moment the coil gets 
into the position of enclosing the maximum num- 
ber of lines the current is reversed in direction, 
what will be the effect ? 



STEAM ENGINEERS AND ELECTRICIANS. 263 

A. The coil will continue to turn in the same 
direction and will make a half turn, after Avhich 
it will stop. 

Q. Can you determine in which direction the 
coil will turn ? 

A. Yes, by applying Fleming's rule previously 
mentioned, using the left hand. Point the fore- 
finger along the positive 
direction of the lines of force 
due to the magnet at any 
part of the coil. Point the 
second finger, held at right <.- 
angles to the forefinger, in 
the direction of the current 
in that part of the coil. 
Finally, extend the thumb 
at right angles to both of the fingers. The direc- 
tion in which the thumb points will be the direc- 
tion in which that part of the coil will move. 

Q. And if at this point the direction of current 
is again reversed ? 

A. The coil will rotate in the same direction one 
half-turn further. 

Q. What piece of well-known electrical appa- 
ratus operates in this manner ? 

A. The electric motor. 

Q. Does it make any difference whether the 
magnet is a permanent or electro-magnet ? 




264 roper's catechism for 

A. None at ail, except that greater strength can 
be secured by usmg an electro-magnet. 

Experiment 7. — Suppose we have the same coil 
of wire as in Experiment 6, which we will call 
^coil No. 1, connected to a galvanometer, and near 
it a second coil attached to a battery. A current 
is flowing through coil No. 2, but not through coil 
No. 1, of course. 

Q. What occurs if we suddenly disconnect the 
battery from coil No. 2, and what does it show ? 

A. The needle of the galvanometer will give a 
sudden jump, showing that by stopping the cur- 
rent through coil No. 2 a current has been pro- 
duced, or induced, as we say, in coil No. 1, 
although coil No. 1 is not connected to coil No. 2 
in any way. In a moment or two the needle of 
the galvanometer will come to rest at its original 
position, showing that the current has ceased. 

Q. What will occur if the battery be again con- 
nected to coil No. 2 ? 

A. The needle will again jump, but this time 
in the opposite direction, showing that the induced 
current is in the opposite direction. 

Q. Suppose that the current instead of being 
entirely stopped were diminished and then in- 
creased, what would happen ? 

A. We should see the needle go first one way 
and then the other, as before, showing that any 



STEAM ENGINEERS AND ELECTRICIANS. 265 

change in the strength of current hi coil No. 2 
tends to induce a current in No. 1. 

Q. Looked at from the standpoint of Hnes of 
force, what has occurred in this experiment ? 

A. From the standpoint of Hnes of force, when 
the current in coil No. 2 is increased more lines 
of magnetic force are enclosed by No. 1, and a 
current is produced. When the current is dimin- 
ished less lines pass through No. 1, and a current 
is induced in the opposite direction. The nearer 
the two coils are to each other the greater the 
effect, and if a soft iron core be introduced into 
the axis of the coils, the induced current becomes 
enormously greater than before. 

Q. What electrical apparatus is illustrated by 
tiiis experiment? 

A. The transformer. 
. Experiment 8. — Connect a battery to a galvanom- 
eter and notice the reading of the needle which 
shows what current is flowing through the circuit. 
Connect in tandem another cell of battery. 

Q. What will occur ? 

A. The reading of the galvanometer needle will 
be increased, being about double what it was 
before. 

Q. What does this show ? 

A. That the current through the circuit is 
double. 



266 roper's catechism for 

Q. Has the resistance of the circuit been appre- 
ciably changed? 

A. No. 

Q. What could have caused double flow through 
the same resistance ? 

A. Reasoning from analogy to the flow of water, 
the pressure tending to cause flow must have been 
doubled. 

Q. Would you then conclude that there is such 
a thing as electrical pressure ? 

A. Yes, and that each generator, as, for instance, 
a battery, furnishes a definite pressure, and that 
when two are connected in tandem the two 
together furnish a pressure which is the sum of 
the pressures furnished by each. 

Q. What other names are there for electric pres- 
sure? 

A. Difference of potential (P. D.), electro- 
motive force (e. m. f. ), and voltage. ■ 

Q. The battery produces electric pressure by 
means of chemical action; is there any other 
method ? 

A. Yes; an electric pressure is produced wher- 
ever a conductor cuts across lines of force; or if the 
conductor is in a coil a pressure is produced when- 
ever the number of lines of magnetic force 
enclosed by the coil is in any way changed. 
The pressure continues only so long as the 



STEAM ENGINEERS AND ELECTRICIANS. 267 

cutting or change of number of lines of force 
continues. 

Q. Upon what does the amount of electric pres- 
sure depend ? 

A. On the rate of cutting the lines of force — 
that is, the number cut per second or the change 
per second in the number enclosed by a coil. 

Q. Suppose a coil has 10,000 lines of force 
passing through it, its plane being perpendicular 
to the lines of force, which lines are in this case 
supposed to be parallel and straight. Now let 
the coil be rotated one quarter- turn, how many 
lines will it enclose ? 

A. Zero. 

Q. Suppose it took one-quarter of a second to 
make the quarter-turn, what would be the rate of 
change of lines of force enclosed by the coil ? 

A. 10,000 ^i = 40,000 per second. 

ELECTRICAL UNITS. 

Q. What is the unit of electrical pressure or 
electro-motive force ? 

A. The volt, which is the pressure furnished by 
a certain standard cell. 

Q. What is the unit of resistance ? 

A. The resistance of a column of mercury 41.85 
inches long and w^eighing 223 grains at 32° Fahr. 
It is called the ohm. 



268 roper's catechism for 

Q. Are the standard ohms and multiples of the 
ohm used in practice made of mercury ? 

A. No; they are made of German-silver wire, or 
an alloy of copper, nickel, and one or more metals. 

Q. What is the unit of current ? 

A. It is the current which will deposit, in one 
second, on the kathode plate, from a standard 
solution of silver nitrate, .001118 gram (.017 
grain) of silver. It is called the ampere^ and is 
in its nature a unit of rate of flow and analogous 
to a flow of a certain quantity per second. 

Q. What other common unit is employed ? 

A. The watt, which is the unit of power. It is 
equal to a volt-ampere ; that is, the power in watts 
is equal to the product of the number of amperes 
flowing multiplied by the number of volts pressure 
causing the flow. 

Q. What relation does the watt bear to a horse- 
power ? 

A. One horse-power equals 746 watts exactly, 
or, in round numbers, 750. 

Q. AVhat multiple of the watt is found con- 
venient ? 

A. The kilowatt, written K.W., which is 1000 
watts and nearly equal to -| horse-power. 

Q. In measuring electrical properties, such as 
current, pressure, resistance, or power, what is the 
general method of going about the work ? 



STEAM ENGINEERS AND ELECTRICIANS. 269 

A. Take current as an example. We find some 
effect of current easy to observe, and we agree to 
call a current which produces this effect to a certain 
extent unit current, as, for example, the current 
which in one second will deposit from a nitrate of 
silver solution .017 grain of silver is called unit 
current. Having an unknown current which it is 
desired to measure, we observe how many grains 
of silver it will deposit in one second, and if it 
deposits . 17 grain we call it a current of 10 units 
or 10 amperes. Of course, no one in actually 
measuring a current now goes through the long 
process of measurement by means of depositing a 
metal any more than in order to measure a length 
he makes a journey to the British Museum to get 
the standard yard-stick. Convenient instruments 
working on the principle of a galvanometer are 
made so that when a current of 1 ampere flows 
through their coils their needle points to 1; with 
a current of 2 amperes, points to 2, and so on. 

Q. What multiples of the units given above are 
in common use? 

A. The megohm = 1 million ohms. 

The microhm = 1 millionth part of 1 ohm. 
The kilowatt = 1 thousand watts. 

Q. Can these prefixes, meg, micro, and kilo, be 
used with the other electrical units ? 

A. Yes; although such use is not very common. 



270 roper's catecpiism for 

RESISTANCE. 

Q. How is the resistance of a conductor affected 
by increasing its length ? 

A. The resistance is increased proportionately 
to the increase in length. 

Q. What is the effect of increasing the area of 
cross-section ? 

A. The resistance is lessened proportionately; in 
other words, the resistance is inversely pro23ortional 
to the area of the cross-section. 

Q. A certain size wire, 100 feet long, has a 
resistance of 2 ohms, — what will be the resistance 
of 200 feet of the same wire ? 

A. 2 X 2, or 4 ohms. 

Q. Suppose that 100 feet of wire -^ inch diam- 
eter has a resistance of 1 ohm, — what would be its 
resistance if the diameter were ^V inch ? 

A. Since the new diameter is one-half the old, 
the area of cross-section of the new wire is J X J, 
or one-quarter that of the old wire. The resistance 
therefore would be four times greater, or 4 ohms. 

Q. What is meant by the conductivity of a wire 
or other conductor ? 

A. The opposite of resistance. It is numeri- 
cally e(^ual to 1 divided by the resistance. 

Q. A wire has a resistance of 100 ohms, — what 
is its conductivity ? 




STEAM ENGINEERS AND ELECTRICIANS. 271 

A. 1-^0 5 01' -Ol- 

Q. When two re- 
sistances, as Fand R, 
are joined as shown 
in the figure, how are 
the}^ said to be connected ? 

A. In parallel or multiple. 

Q. When so connected, what is their joint 
resistance, that is, the resistance from A to B? 

A. It is found by the formula, joint resistance 

~ E-i- Y' 

Q. Two resistances of 10 and 20 ohms respect- 
ively are joined in multiple, — what is their joint 
resistance ? 

, 10 X 20 200 .2 I. 

^- I0-+20^W==^^^^^^- 

Q. When the resistances are equal, what is the 
joint resistance ? 

A. One-half the resistance of one. 

Q. When several equal resistances are connected 
in multiple, what is their joint resistance equal to ? 

A. To the resistance of one divided by the 
number of them. „ , 

Q. When are two conductors said to be con- 
nected in series f 

*For complete explanation, see "Eoper's Engineers' 
Handy-Book," page 665. 



272 koper's catechism for 

A. When they are jomed tandem, or end on. 

Q. When two resistances are connected hi series, 
what is their Joint resistance equal to ? 

A. To the sum of the separate resistances. 

Q. What is specific resistance ? 

A. It has the same relation to resistance that 
specific gravit}^ has to weight. It is the resistance 
of a cubic inch, or it may be expressed in cubic 
centimeters. 

Q. What are some of the substances having 
large specific resistance ? 

A. Of the metals — lead, mercury, and alloys. 
The non-metals have a much higher specific resist- 
ance. 

Q. What are some substances having a low 
specific resistance ? 

A. Copper, silver, and gold. 

Q. What are non-conductors ? 

A. Substances having a high specific resistance. 

Q. What are conductors ? 

A. Substances having a low specific resistance. 
The metals are classed as conductors and the non- 
metals as non-conductors. 

Q. What are insulators ? 

A. " Insulators " is another name for non-con- 
ductors or poor conductors. 

Q. What effect does a change of temperature 
have on the resistance of substances ? 



STEAM ENGINEERS AND ELECTRICIANS. 



273 



TABLE OF RELATIVE RESISTANCES. 

(Substances Arranged in Order of Increasing .Resistance for 
SAME Length and Sectional Area.) 



Name of Metal. 



Silver, annealed, . . 

Copper, annealed, . 

Silver, hard dravrn. 

Copper, hard drawn, 

Gold, annealed, , . 

Gold, hard drav^'n, . 

Aluminum, annealed, 

Zinc, pressed, . . . 

Platinum, annealed, 

Iron, annealed, . . 

Gold-silver alloy (2 ozs. gold, 
1 oz. silver), hard or an- 
nealed, 

Nickel, annealed, 

Tin, pressed, 

Lead, pressed, . 

German silver, hard or an- 
nealed, 

Platinum-silver alloy (1 oz. 
platinum, 2 ozs. silver), 
hard or annealed, . . . . 

Antimony, pressed, . . . . 

Mercury, 

Bismuth, pressed, 

Carbon, 



Resistance in Microhm 

at 0° Centigrade. 

32° Fabr. 



Cubic 
Centi- 
meter. 



1.504 
1.598 
1.634 
1.634 
2.058 
2.094 
2.912 
5.626 
9.057 
9.716 



10.87 
12.47 
13.21 
19.63 

20.93 



24.39 
35.50 
94.32 
131.2 



Cubic 
inch. 



0.5921 

0.6292 

0.6433 

0.6433 

0.8102 

0.8247 

1.147 

2.215 

3.565 

3.825 



4.281 
4.907 
5.202 

7.728 

8.240 



9 603 
13.98 
37.15 
51.65 



Relative 
Resist- 
ance. 



1. 

1.063 

1.086 

1.086 

1.369 

1.393 

1.935 

3.741 

6.022 



7.228 
8.285 
8.784 
13.05 

13 92 



16.21 
23.60 
62.73 

87.23 
14. 



18 



274 EOPER's CATECHISM FOR 

A. It increases the resistance of metals and 
diminishes the resistance of non-conductors. 

Q. Can you remember about how much a 
change of temperature of one degree Fahrenheit 
affects the resistance of metals ? 

A. It increases the resistance of the common 
metals roughly about 2 parts in 1000. 

Practical Use of Conductors and Insulators. 
— For carrying electrical energy from the point 
where it is generated to the point where it is to be 
used we want to use such material and of such 
size that the resistance of the circuit does not 
exceed reasonable limits, although we must be 
guided by consideration of the first cost. Copper 
has the lowest specific resistance of the common 
metals and is generally employed, although if 
aluminum gets much lower in price than now 
(30 cts. per pound), it will be a serious competi- 
tor to copper. Iron is used only on short tele- 
graph and telephone lines. It is evident that the 
circuit should be as direct as possible, as the 
greater its length the greater its resistance, and 
therefore the greater is the amount of energy lost 
on the line. 

Insulators are used to prevent current from 
being led off the conductors. For all work ex- 
cept outdoor work, and, indeed, for a large part 
of that, the conducting wire is covered with one 



STEAM ENGINEERS AND ELECTRICIANS. 275 

or more layers of some compomid of rubber 
which is a good insulator. The thicker this 
rubber covering the better its insulating proper- 
ties, for we have made the path of leakage of 
current longer by thickening the rubber coating. 
A further protection is given by suspending the 
wires at intervals on porcelain or glass or other 
insulators, so that the wire only comes in contact 
with its coating, porcelain, or the air, which is 
also an exceedingly good insulator. To sum up 
briefly, make the path through which you want 
the current to flow as short and easy as possible. 
Make all possible leakage paths as long and nar- 
row as possible. 

CUEEENT. 

Q. What are some of the most notable effects 
of electric current ? 

A. It heats the conductors which carry it; it 
produces around the wire a magnetic field which 
exerts a force on all magnetic substances placed 
within the field; it has the power to decompose 
or electrolyze solutions of many chemical com- 
pounds. To these three effects are given the 
names heating effect, magnetic effect, and electro- 
lytic effect. 

Q, Is the heating effect proportional to the 
strength of current or number of amperes ? 



276 roper's catechism for 

A. No; if the amperes are doubled the heating 
effect is four times as great instead of twice as 
great. With three times as many amperes the 
heating effect is nine times as great. 

Q. What is the law, then, which connects the 
heating effect with the strength of current ? 

A. The heating effect is proportional to the 
square of the current strength. 

Q. How is the heating effect of a certain cur- 
rent affected if the resistance through which it 
flows is doubled ? 

A. The heating effect is doubled, it being 
strictly proportional to the resistance. 

Q. Is there any formula which gives the num- 
ber of heat units produced by a certain current 
through a certain resistance ? 

A. Yes; in " Roper' s Engineers' Handy-Book," 
page 670. 

Q. Is the heating effect of a current a source of 
danger ? 

A. It may be; if wires which carry currents 
are too small they may be so heated as to set fire 
to neighboring woodwork. On this account the 
insurance underwriters have found it necessary to 
prescribe the minimum sizes which shall be used 
for various currents. These are published in 
tables called ' ' Tables of Safe Carrying Capacity 
of Wires." 



STEAM ENGINEERS AND ELECTRICIANS. 277 

Q. Is any practical use made of the heating 
effect of the electric current ? 

A. Yes; in electric heaters and cooking devices, 
and also in the incandescent lamp, where the fila- 
ment is heated white hot. 

Q. Is the magnetic effect of a current propor- 
tional to the current strength ? 

A. Strictly. 

Q. Is the electrolytic effect also proportional to 
the current strength ? 

A. Yes; doubling the number of amperes will 
always double the electrolytic effect, tripling the 
amperes will triple it, and so on. 

Q. When, as in Experiment No. 1, a metallic 
salt is electrolyzed, does the amount of copper 
deposited bear any definite relation to the current 
strength ? 

A. Yes; one ampere will always deposit a 
definite amount of copper per second. 

Q. Does it make any difference what salt of 
copper is used ? 

A. Generally speaking, no; but with one or 
two salts the number of grains of copper deposited 
per second by one ampere is double what it is 
with the ordinary salts. 

Q. Will one ampere deposit from a silver salt 
solution the same number of grains per second as 
with copper? 



278 roper's catechism for 

A. No; one ampere deposits different weights 
of the various metals per second, the amounts 
being proportional to the atomic weights of the 
elements * or to multiples of them. 

ELECTRO-MOTIVE FORCE OR ELECTRIC 
PRESSURE. 

Q. In what ways may electric pressure be pro- 
duced ? 

A. There are many ways of which these four 
are the most common: 

1. By rubbing together two dissimilar sub- 
stances, as silk and glass. 

2. By heating the point at which two dissimilar 
metals are joined together. 

3. By chemical action, as in Experiment No. 1 
with the chemical battery. 

4. By moving a magnet relatively to a coil of 
wire, as in the dynamo, the principle being illus- 
trated in Experiment No. 4. 

Q. Which method is the most important? 

A. The last; the first two are scarcely used at 
all in practice. The third is used only where 
small amounts of power are required. 

Q. If there is a difference of electrical pressure 
existing between two points and these two points 
be joined by a conductor, what will occur ? 
*See " Roper's Engineers' Handy-Book," p. 612. 



STEAM ENGINEERS AND ELECTRICIANS. 279 

A. An electric current will flow from the point 
of higher pressure to the other point. 

Q. How long will this current continue? 

A. As long as there is any difference of pressure 
between the two points. If the two points are, for 
example, the terminals of a battery, which by 
chemical action keeps up a difference of pressure 
between its terminals, the current would continue 
until one of the chemicals of the battery, the zinc 
or solution, is exhausted. 

Q. How could you determine if two points 
were at the same pressure ? 

A. By connecting a galvanometer between the 
points. If the needle of the galvanometer was 
not deflected this would show that no current 
flowed through it and, therefore, that no difference 
in electrical pressure existed between the two 
points to which it was connected. 

Q. When an electric pressure exists between two 
points, is there also any mechanical pressure. 

A. Yes; the medium or substance separating 
the two points is under a mechanical strain which 
is proportional to the number of volts electrical 
pressure existing between the two points. If this 
voltage is very great the substance, be it air, glass, 
porcelain, or otherwise, is actually cracked and an 
electric spark passes which tends to relieve the 
difference of pressure. 



280 roper's catechism for 



OHM'S LAW. 

This law, which is the relation existing 
between current, pressure, and resistance of a 
circuit, is the most important law in electrical 
science, and an intelligent application of it will 
solve most problems which the ordinary engineer " 
will meet. This law is as follows: In an electric 
circuit the total current (amperes) is equal to the 
total electric pressure (in volts) divided by the 
total resistance (in ohms). In shorter form it is 

E 

expressed by the formula O = 75-, where C = cur- 

rent in amperes, E = pressure in volts, and E = 
resistance in ohms. Several examples will illus- 
trate its use. 

Q. In a certain electrical circuit there is an 
electro-motive force or electrical pressure of 4 volts. 
The total resistance of the circuit is 2 ohms. 
How much will be the current ? 

E 

A. (7 = -^ = f = 2 amperes. 

Q. What electro-motive force or electrical pres- 
sure must be used to force a current of 10 amperes 
through a circuit whose resistance is 10 ohms ? 

A. C=~otE=CR = 10x10 = 100 volts. 
K 

Q. If under a pressure or electro-motive force 



STEAM ENGINEERS AND ELECTRICIANS. 281 

of 100 volts we get a current flow of 20 amperes, 
what is the resistance of the circuit ? 

A. C=^OYR = ^ = ^'- = 5ohms. 

When there is more than one electro-motive 
force acting in a circuit, we must use for the value 
of E in the above formula the resultant of all the 
separate electro-motive forces acting. When there 
are several resistances in a circuit their joint 
resistance must be used. 

Q. Suppose we have two batteries, one giving 
2 volts and the other 1 volt, their plates being zinc 
and carbon, but different solutions being used in 
each. Connect the zinc of one to the carbon of 
the other, and then connect from A to B a piece 
of wire having a resistance 
of, say, 10 ohms, as shown 
in the sketch. When con- 
nected in this way the elec- 
tro-motive forces are added, c^JuuumMJiuum} 

and the total electro-motive 1^^ — /oohms ji 

force is 2 -f- 1, or 3 volts. The batteries themselves 
have some resistance, and also the lead wires A C 
and B D. Suppose that the resistance of one bat- 
tery is 4 ohms and the other 2 ohms, the resist- 
ance of A and B D each 1 ohm. Then the 
total resistance of the circuit is 10 + 1 + 2 -(- 4 
+ 1 = 18 ohms. What will be the current? 



^b 



282 

A. The current will be 



roper's catechism for 

resultant E 



Totalis 18 — 6 



tt 



[XWUULUSJLSiWiSJUUU 



ampere. 

Q. Suppose that one of the batteries was re- 
versed so that the two zincs are 
connected together as in the 
sketch ? 

A. The batteries now oppose 
each other and the resultant or 
effective electro-motive force is 
2 — 1, or 1 volt. The resistance of the circuit is, 
as before, 18 ohms, and the current will be -^ 
ampere. 

Calculation of Current in Divided Circuits. 

— Suppose that the battery has an electro-motive 

force of 2 volts, that its 

resistance is J- ohm, that 

the resistance of the lead 

wire A B is S ohms, and 

that between C and B we 

have two paths of resistance 10 and 20 ohms each. 

Q. What will be the total current flowing 

through the batter}^ and through A Bf 

A. First find the total resistance of the circuit. 
The joint resistance between the points B and E 
is, as previously shown under ' ' Resistance, ' ' 
10 X 20 



equal to 



10 + 20 



: ^0 ^ g| ol^j^g^ rpj^g ^(j^al 



STEAM ENGINEERS AND ELECTRICIANS. 283 

resistance of the circuit is therefore 6f + J + 3, 

E 

or 10 ohms. The current is equal to p = ^^ ^ .2 

ampere. 

Q. What part of the current flows through 
each branch ? 

A. Obviously the greater part of the current 
will flow through the branch having the smaller 
resistance. ^^ or J- ampere will flow through the 
20 ohms branch, and f-J or f ampere will flow 
through the other branch. 

Practical Approximation. — If the resistance 
of batteries or generator and the leads is small 
compared to that of the main resistance in circuit, 
we may neglect them, using for R in the formula 
the resistance of the external circuit. This is 
generally the case in electric lighting circuits, 
where the resistance of the generator will rarely 
exceed one-hundredth of an ohm, and where the 
resistance of the line wires will usually be less than 
one-twentieth of the joint resistance of the lamps. 

Example. — Q. On a 110- volt circuit, what is the 
current (total) when one sixteen-candle-power 
lamp of 220 ohms' resistance is turned on ? 

A. E= 110, R is practically 220 ohms. The 
current = ^^ = ^ ampere. 

Q. What is the current (total) when two lamps 
are turned on ? 



284 roper's catechism for 

A. The joint resistance of two similar lamps is 
220 X 220 220 X 220 .,r. . . w 

2-20T220 = TT220- = ^^^ ^^^^^^' '' '"^^ 
that of one lamp. The total current = {{% = 1 
ampere. The current through each lamp is the 
same, and is ^ ampere as before. 

With three lamps turned on the joint resistance 
is one-third of 220, or 73J, and the total current 

^______ ^^ ^^^ "" ^^ ^^^~ 

r~ r~~ 1.^^ peres, and the cur- 

r^ r^ r ^ ^^^^ through each 

lamp is still ^ am- 
pere. Turning on one lamp then adds J ampere 
to the total current. The lamps are connected in 
multiple as shown in the figure. 

The Use of Alternating Currents complicates 
the calculation of current, pressure, and resist- 
ance by Ohm's laAv, and the method of making 
such calculations is outside of the scope of this 
book, inasmuch as the ordinary engineer would 
rarely be called upon to do so. 



STEAM ENGINEERS AND ELECTRICIANS. 285 



ELECTRICAL MEASUREMENT. 

Q. What are the electrical quantities which the 
engineer is called upon to measure ? 

A. Current, electro-motive force, resistance, and 
power. 

Q. What instruments are necessary ? 

A. For direct-current circuits, an ammeter and 
voltmeter of proper range. 

Q. How are the Weston ammeters constructed ? 

A. They consist of a fixed permanent magnet 
of horse-shoe form, between the poles of which is 
pivoted a coil of fine wire which carries the needle. 
When the coil is connected so that a current flows 
through the coil, it tends to turn so as to include 
the maximum number of lines of force due to the 
magnet. This motion is resisted by a pair of 
springs resembling the hair spring of a watch. 

In the instruments for measuring currents of 
mdre than an ampere, only a known fraction of 
the current passes through the coil, the balance 
passing through a conductor placed in parallel 
with the coil. 

Q. Suppose we have a circuit similar to that in 
the sketch and we desire to measure the current 
taken by four lamps. How would you proceed ? 

A. If these are 16 candle-power (16 c. p.) 



286 



ROPER'S CATECHISM FOR 



lamps on a 110-volt circuit, we know that they 
will take, roughly, J ampere each. Therefore to 
measure accurately their current we need an 
ammeter intended to measure small currents. 
Connect its terminals to two points on the circuit 
as C and D by wires, as shown by dotted lines. 
Then cut the circuit between C and D. The total 
current will now flow around through the am- 
meter and the reading of the needles will, if the 
instrument is correct, give 



the current in amperes. 
Notice that one termi- 
(^5*25 ^^^ ^^ marked + and the 
other — . If the instru- 
ment is not connected 
properly, the needle will 
move, or try to move, to 
the left of the scale. In 
this event reverse the wire connections from the 
points C and D to the instrument. Such an 
instrument tells the polarity of the circuit — that 
is, which is the higher pressure and which the 
lower pressure side. When the + binding-post 
is connected to the higher pressure side of the 
circuit the needle deflects in the proper direc- 
tion. 

Q. Suppose we have no ammeter of proper 
range available, but we have a resistance whose 



STEAM ENGINEERS AND ELECTRICIANS. 287 

value we know and which will carry the current 
to be measured without much heating ? 

A. In this case with the aid of the voltmeter 
we can measure current. Suppose we have a 
resistance which we know is 1 ohm and a portable 
voltmeter with an additional scale reading from 
to 15 volts, and we want to make the current- 
measurement just described. Put the resistance 
in between C and D and connect the voltmeter 
terminals to the ends of the resistance. Suppose 
the reading of the voltmeter was 2.3 volts. The 
current through the resistance is by Ohm's law 
equal to the electrical pressure or electro-motive 
force between its terminals divided by the resist- 
ance, or 2. 3 ^- 1, which is 2. 3 amperes. This is the 
method used in the Weston switchboard instru- 
ments, a resistance of known value being placed 
in the main circuit of the dynamo and two leads 
taken off from its terminals and run to a volt- 
meter. 

Q. How would you measure the electrical pres- 
sure between two points ? 

A. I would connect the terminals of a voltmeter, 
one to each of the points. 

Q. Suppose the voltage between the points is 
greater than the range of the voltmeter. For 
example, suppose you wish to measure a voltage 
which you know is about 220, but have an instru- 



T-/ 



V* 



288 roper's catechism for 

ment which reads only to 150 volts, what is the 
inethod ? 

A. Connect between the two points A and B, 
whose voltage is wanted, 
two 110- volt lamps in se- 
ries. Then make the con- 
nections shown by the solid 
lines and read. Change 
" the connections to the dot- 

ted positions and read again. The sum of the two 
readings will be the voltage between A and B. 
Q. Is there any other method ? 
A. Yes; in the other method it is necessary to 
have a known resistance, to place it in series with 
the voltmeter, and also to know the resistance of 
the voltmeter. This last is usually given on the 
box containing the instrument. A resistance just 
equal to that of the instrument doubles its range. 
In general, to get the value of the reading of a 
voltmeter when a resistance has been put in series 
with it, multiply its reading by the sum of the 
resistance of the instrument and the auxiliary 
resistance, and divide the product by the resistance 
of the instrument. 

Q. How would you measure a resistance ; for 
instance, the resistance of a coil of wire ? 

A. li I had an ammeter and voltmeter of 
proper range I would put the ammeter in series 



STEAM ENGINEERS AND ELECTEICIANS. 289 

with the coil and would connect the voltmeter to 
its terminals. Then I would send a current from 
a battery or dynamo through the coil and take the 
readings of the ammeter and voltmeter. By 

Ohm's law current = — ^-—^ — or resistance = 
resistance 

voltage 

current' 

Q. What do you mean by instruments of proper 
range in this case ? 

A. The ammeter must be suitable for measur- 
ing the largest current which the coil can carry 
without overheating, and the voltmeter must be 
such that the voltage at the terminals of the coil 
will give a deflection of the need large enough to 
be readable with accuracy. 

Q. Is there any other method of measuring 
resistance ? 

A. Several. One of the most valuable, since it 
needs only a voltmeter of known resistance and 
some form of current 



X 



,.^y^^"^^^ 






generator, is known as 
the Voltmeter Method. 
This method requires 
two readings of the 
instrument. For the 
first reading the in- 
strument is connected to the terminals of the 
19 • 



290 roper's catechism for 

current-generator. For the second reading the 
unknown resistance is put in series with the volt- 
meter and then the two connected to the generator. 
In the figure X is the unknown resistance, and for 
the first reading the connection shown by the 
dotted hne is made. For the second reading the 
connection is as shown by the solid lines. To cal- 
culate the resistance from the readings divide the 
first reading by the second, then multiply the 
quotient by the resistance of the voltmeter, and 
from the product subtract the resistance of the 
voltmeter. 

Q. Which of these methods would you use for 
low resistances of, say, less than 100 ohms ? 

A. The first method. 

Q. Which for high resistances, such as insula- 
tion tests ? 

A. The voltmeter method. 

Q. How would you connect for a test of the 
insulation of the armature 
coils of a dynamo, from 



''' ' the frame ? 



A. As in the figure, the 
heavy black line represent- 
ing a commutator seg- 
ment, and the cross-hatched 
portion representing the frame. The white space be- 
tween, of course, represents the insulating material. 



STEAM ENGINEERS AND ELECTRICIANS. 291 

Q. How would you measure the power used in 
any part of a circuit, as, for example, in a lamp ? 

A. Power being the product of volts by amperes 
(in direct-current circuits), I would connect an 
ammeter in series with the lamp and a voltmeter to 
its terminals, and would multiply their readings 
together, thus obtaining the number of watts. 

Q. Suppose you wished to get the horse-power ? 

A. I would divide the number of watts by 
746. 



292 roper's catechism for 



ELECTRIC BATTERIES. 

Q. What two kinds of electric generators are 
in most common use ? 

A. The chemical generators, or batteries, and 
the magneto- electric generators, or dynamos. 

Q. In what cases are batteries used? 

A. When the amount of power to be supplied 
is small, as for bells, time clocks, telegraphs, tele- 
phones, surgical lamps, dental engines, etc., and 
in some cases in which the introduction of the 
engine which would be needed to drive a dynamo 
would be objectionable. 

Q. Why are batteries not used when large 
amounts of power are required ? 

A. On account of the expense of the chemicals 
used. Zinc is in nearly all batteries the fuel, and 
since the energy produced by burning one pound 
of it is only one-sixth that produced by one pound 
of coal, and, moreover, since the cost of zinc is 
about sixty times that of coal, it is much cheaper 
to generate electric power by means of coal rather 
than by means of zinc. 

Q. What are secondary or storage batteries ? 

A. Those whose chemical actions may be re- 
versed by sending an electric current (from some 
outside source) through them in the opposite 



STEAM ENGINEERS AND ELECTRICIANS. 293 

direction to the current which they have produced. 
Thereby they are restored to the original condition 
which existed before they were used to produce 
electric current. 

Q. Do they store electricity ? 

A. Not at all. They store up energy in the 
form of chemical energy, which at any time may 
be changed into electrical energy by connecting the 
terminals of the battery together by some con- 
ductor. 

Q. What are primary batteries ? 

A. Those whose chemical actions cannot be 
reversed by passing an electric current through 
them in the reverse direction. 

Q. Give an example of a reversible cell. 

A. The Daniell cell. 

Q. Is it used as a storage or as a primary battery ? 

A. As a primary; others being better adapted 
for use as secondaries. 

Q. Into what two classes may primary cells be 
divided ? 

A. OiDcn-circuit cells and closed-circuit cells. 

Q. What is an open-circuit cell ? 

A. A cell suitable for use on circuits that are 
normally open, being closed only at the moment 
when work is to be done; as, for example, bell 
circuits, gas-lighting circuits, time systems, watch- 
clock systems, etc. 



294 roper's catechism for 

Q. What kind of a cell is generally employed 
for such work ? 

A. A cell known as the Leclanche, having a 
zinc plate for one pole, a carbon plate for the 
other pole, and the two immersed in a solution of 
sal-ammoniac. 

Q. What is the voltage furnished by such a cell 
and what is the resistance of the ordinary size 
cell? 

A. About IJ- volts and from -^-^ to -f^ ohm 
resistance. 

Q. Why is not this cell suitable for closed cir- 
cuit work ? 

A. Because when a circuit is closed hydrogen 
particles begin to collect on the carbon plate, and 
these cut down the voltage and at the same time 
increase the resistance of the cell. 

Q. If the circuit of the cell is opened do these 
disappear ? 

A. Yes; in a few minutes. 

Q. Is there any way of lessening the trouble 
caused by the collection of hydrogen particles ? 

A. Yes; by using a porous carbon and by put- 
ting next to the carbon a slab of some strong 
oxidizing agent like manganese binoxide. In the 
best forms of cell the carbon is made in the form 
of a thin, hollow cylinder, and the manganese in 
powdered form is placed inside. 



STEAM ENGINEERS AND ELECTRICIANS. 295 

Q. What is the effect of the manganese bin- 
oxide ? 

A. It gives up a part of its oxygen, which 
attacks the hydrogen particles and forms, with 
them, water. 

Q. Why are some zincs made in the form of a 
hollow cylinder extending around the carbon ? 

A. To diminish the resistance of the cell. The 
greater the surface of the plates and the nearer 
they are together, the less is the resistance of the 
cell. 

Q. What cell is largely used for closed circuit 
work? 

A. Some form of the Daniell cell. In its orig- 
inal form it consisted of a zinc plate in sulphuric 
acid on one side of a porous wall and a copper 
plate in a solution of copper sulphate on the 
other side. 

Q. What is the gravity cell ? 

A. A form of Daniell in which the different 
specific gravities of the liquids are used to keep 
the liquids from mixing without the use of a 
porous cup. 

Q. What is the voltage and resistance of a 
Daniell cell ? 

A. The voltage is about 1 volt. The resistance 
of the ordinary size gravity is in the vicinity of 4 
ohms. 



296 roper's catechism for 

Q. What other cell is largely used and for what 
class of work? 

A. The bichromate cell; for small motors and 
cautery work, where a strong current is needed for 
a few minutes. It consists of zinc and carbon 
plates immersed in chromic acid. 

Q. What is the voltage of these cells and their 
resistance ? 

A. About 2 volts. Their resistance varies, of 
course, with their size, that of the smaller sizes 
being only a fraction of an ohm. 

Q. What are the two chief objections to this cell ? 

A. The fumes produced and the eating, of zinc 
even when the circuit is open. 

Q. What is done to lessen the latter objection ? 

A. The cell is arranged so that the zinc ■ plate 
can be easily raised out of the solution when the 
circuit is open. 

Q. What are dry cells ? 

A. Cells in which the solution has been reduced 
to a pasty condition. 

Q. What are their advantages ? 

A. Their greater portability; on the other hand, 
their resistance is higher, and they polarize more 
readily. 

Q. What do you mean by polarization? 

A. The collecting of hydrogen particles previ- 
ouslv mentioned. 



STEAM ENGINEERS AND ELECTRICIANS. 297 

DYNAMOS* 

Q. For what is a dynamo used ? 

A. To change mechanical energy into electrical 
energy. 

Q. The dynamo as well as the battery are 
sometimes likened to an electrical pump. In 
what respect do they resemble a pump ? 

A. They may be considered as raising electricity 
from a low level to a high level, just as a pump 
raises water. 

Q. Of what does a dynamo consist ? 

^. Of a magnet and a coil of wire moving 
relatively to each other. Generally, the magnet 
is fixed and the coil rotates between its poles. A 
difference of electric pressure is set up between the 
two ends of the coil, and if these ends are connected 
together a current will flow. 

Q. Upon what does the amount of electrical 
pressure depend? 

A. It is proportional to the rate of change in 
the number of lines of force enclosed by the coil. 
It is, therefore, increased by increasing the strength 
of the magnet, the speed of revolution, or the 
number of turns of wire in the coil. 

Q. With such a simple dynamo, is the direction 
and strength of current uniform ? 



298 eoper's catechism for 

A. No; the current can best be represented by 
plotting its values at different moments, as in the 
figure. Here distances to the right along the 
horizontal line represent time. Distances above 
or below the line represent the strength of current 
at different times. The curve shows the variation 
of current during three complete revolutions of 
the coil. It is evident from this curve that the 
strength of current is alwaj^s changing and that it 
changes direction twice in each revolution. * 






Q. What is such a current called ? 

A. An alternating current. 

Q. Can it be used for practical purposes ? 

A. Yes; for lighting and for small motors. 

Q. How is the current rectified or made contin- 
uous in direction in the circuit where it is to be 
used? 

A. By the commutator, a purely mechanical 
device which changes the connection between the 
ends of the coil and the external circuit just at the 
moment that the direction of the current in the 
coil is reversed. 

* See also ' ' Roper's Engineers' Handy-Book, ' ' page 689. 



STEAM ENGINEERS AND ELECTRICIANS. 299 

Q. What is a rectified current called ? 

A. A direct current. 

Q. For what purposes is it employed ? 

A. For nearly all isolated lighting plants, for 
operating most arc lights, for driving motors, and 
for charging storage batteries. 

Q. What is the moving coil called ? 

A. The armature. 

Q. How does it differ in practice from the ideal 
simple dynamo ? 

A. The armature is made up of a large number 
of coils wound on an iron core. The larger num- 
ber of coils give greater uniformity to the strength 
of current and diminishes the sparking at the 
commutator. The iron core is used to keep as 
many as possible of the lines of force produced 
by the magnet in the space in which the armature 
is moving, thus making the electrical pressure 
higher than would be the case without the iron core. 

Q. How is the iron core made ? 

A. Of thin circular disks held together by bolts 
and attached to the armature shaft by a sort of 
spider. 

Q. What two classes of armatures are there ? 

A. The Gramme ring and the drum-wound.^ 

Q. What is the reason of making the core out 
of disks instead of solid metal ? 

*See " Roper's Engineers' Handy-Book," page 691. 



•300 



ROPER'S CATECHISM FOR 



A. To diminish the heating of the core by use- 
less currents set up in the core. 

Q. Are the disks separated from each other in 
any way ? 

' A. They are insulated from each other by 
enamel or by thin sheets of varnished paper. 

Q. Is the field magnet of the dynamo a perma- 
nent or electro-magnet ? 

A. An electro-magnet excited by coils carrying 
either a part or all of the current supplied by the 
dynamo. 

Q. What is a series machine ? 




SERIES MACHINE. 

























1 
I 


SI 


;o)^ 


eui 


^ 





SHUNT MACHINE. 



A. A dynamo in which the field-magnet coils 
carry all the current produced by the machine — 
that is, the current flows around the field-magnet 
coils before going to the external circuit. 

Q. What is a shunt dynamo ? 



STEAM ENGINEERS AND ELECTRICIANS. 



301 




COMPOUND MACHINE. 



A. One in which only a fraction of the current 
is had around the field-magnet coils. 

Q. What is a compound 
dynamo ? 

A. A combination of shunt 
and series. 

Q. What are the purposes 
for which a series dynamo is 
used? 

A. A series dynamo tends 
to produce a current of con- 
stant strength whatever load 
may be thrown on it. It is therefore used for 
constant-current circuits such as street arc lighting. 

Q. When is the shunt machine used ? 

A. When a machine is desired which will supply 
constant pressure at all loads. 

Q. Does a shunt machine do this ? 

A. Quite well, but if the closest regulation for 
constant pressure is desired a compound machine 
is used. 

Q. What is an over-compounded machine ? 

A. One which, instead of maintaining the pres- 
sure constant as the load increases, will raise the 
pressure a few volts proportionally to the amount 
of load. 

Q. What is the advantage of this ? 

A. There are two advantages. One is to make 



302 roper's catechism for 

up for a slight lowering of speed in the engine, 
which takes place as the load increases. The other 
is to make up for the loss in pressure owing to the 
resistance of the external circuit wires, which loss 
is proportional to the load which they carry. 

Q. How can the pressure furnished by a shunt 
or compound dynamo be varied ? 

A. An adjustable resistance called a rheostat is 
connected in series with the shunt-field coils; by 
turning the arm of the rheostat in one direction 
more resistance is thrown into this circuit and the 
current flowing around the coils is diminished. 
This cuts down the number of lines of force pro- 
duced by the field magnet, and therefore the pres- 
sure furnished by the machine is lowered. Mov- 
ing the rheostat arm in the other direction raises 
the pressure by cutting out resistance. 

Q. AVhat are the brushes ? 

A. The brushes are pieces of copper or carbon 
resting on the commutator and serving to take 
current from the commutator to the external 
circuit. 

Q. In order to secure freedom from sparking 
what care must be exercised in setting the brushes ? 

A. The brushes must be opposite each other, 
and must fit the surface of the commutator prop- 
erly. The rocker arm carrying them must be 
turned into the position of least sparking. 



STEAM ENGINEERS AND ELECTRICIANS. 303 



DISTRIBUTION OF ELECTRICAL 
ENERGY. 

The production and distribution of electrical 
energy are very much like a small water-system, 
where water is pumped from a tank to a high 
reservoir, taken from the reservoir through pipes 
to the place where it is to be used, and after use 
led back to the tank to be again pumped up and 
again used. The generator, or dynamo, driven by 
a steam engine, gas engine, or water-wheel, corre- 
sponds to the pump. The distributing-pipes in 
the water-system are replaced by copper wires for 
the electrical system. The high-pressure reservoir 
and low-pressure tank are replaced by the switch- 
board bus bars, one of which is a high-pressure 
and the other a low-pressure bar. The high-pres- 
sure^ bar is also called the positive or plus ( + ) 
bar, and the other the negative or minus ( — ) bar. 
They are each copper bars mounted on the marble 
or slate of which the switchboard is made, and 
are called bus bars, or omnibus bars, from the fact 
that all the current is carried by them. The 
valves of the water-system are replaced by switches, 
the water-meters by ammeters, and pressure- 
gauges by voltmeters. Some devices which are 
used in electrical distribution have nothing similar 



304 roper's catechism for 

to them in Avater- systems, but the general shni- 
larity is of great assistance in understanding 
electrical distribution. 

Q. What is a switchboard ? 

A. One or more slate or marble slabs mounted 
on an iron or wooden framework and containing 
the various devices for controlling the electric dis- 
tribution system. 

Q. What are the principal devices to be found 
on the switchboard ? 

A. 1. A voltmeter to measure electric pressure. 
This is generally furnished with a switch by which 
it may be connected to the terminals of any gene- 
rator or to the bus bars. 

2. An ammeter for each generator to measure 
the current which it furnishes. 

3. A rheostat for each generator placed in series 
with its shunt-field coils and controlling the pres- 
sure furnished by it. 

4. A device for each machine, such that if 
owing to any trouble a current greater than the 
maximum for which the machine is designed 
flows through the machine, it is automatically 
disconnected from the circuit. This device may 
be a fuse or a circuit breaker. 

5. A device called a ground detector^ for showing 
when the conductors in the system are by accident 
brought into electrical connection with the earth; 



STEAM ENGINEERS AND ELECTRICIANS. 305 

that is to say, with gas- or steam- or water-pipes 
which are imbedded in the earth. 

6. Switches for disconnecting the generators 
from the bus bars. 

7. Switches for disconnecting from the bus bars 
the distribution circuits. 

8. A device (either fuse or circuit breaker) for 
protecting each distribution circuit from having 
too much current flow over it. 

Q. What are fuses ? 

A. Strips of an alloy, generally of tin and lead, 
of such size that they will melt and interrupt the 
circuit when a current in excess of a certain amount 
flows through them. 

Q. What are circuit breakers ? 

A. Switches so arranged that they open auto- 
matically when the current flowing through them 
exceeds a certain value.* 

Q. Why are circuit breakers used in preference 
to the much cheaper fuses ? 

A. Because in large sizes fuses are very uncertain 
in their action ; a fuse designed to melt at 500 
amperes, for example, being liable to melt with a 
current of 400 or 600 amperes. 

Q. How is a simple form of ground detector 
made, and how does it operate on a circuit, say, 
whose pressure is about 110 volts? 

*See "Roper's Engineers' Handy-Book," page 705. 
20 



306 



ROPER S CATECHISM FOR 



Uu^ 



A. The ground detector consists of two 110-volt 
lamps connected in series with each other and across 
or between the bus bars. The junction between the 
two lamps is connected to a convenient water-pipe. 
So long as the insulation of the circuit is all right 
the two lights burn alike equally dim, since they 
are designed for 110 volts at their terminals and 
they have only 55 volts under the circumstances. 
But suppose any point on the circuit, as P, is 
purposely or accidentall}^ connected 
to earth, then the left-hand light 
will burn bright while the right- 
hand one will burn exceedingly 
dim, or perhaps not at all. The 
reason is that the grounding of the 
point P has put it in electrical 
connection with the point A 
through a very low resistance. 
The current through the right-hand 
lamp is, therefore, diminished, its terminals being 
short-circuited. The left-hand lamp will have 
practically 110 volts between its terminals, since 
the joint-resistance of the right-hand lamp and the 
other path from A to P is exceedingly small, and 
hence the pressure used up being also exceedingly 
small. If the point P were on the other side of the 
circuit, the right-hand lamp would burn brightly 
and the left-hand one ver}^ dimly. 



STEAM ENGINEERS AND ELECTRICIANS. 



307 



Q. How would you find the location of the 
ground ? 

A. By opemng the switches one by one till one is 
found which on being opened relieves the ground. 
This tells on which feeder the ground exists. Then 
the circuit is examined in detail by means of a 
magneto- bell, it being split up into sections by 
throwing open local switches, taking fuses out of 
local distribution boards, and disconnecting at fix- 
tures. 

Q. May any number of dynamos be connected 
in multiple so as to feed on the same pair of 
bus bars ? 

A. Any number of shunt machines of the same 
voltage may be so used. 

Q. Cannot compound machines be so connected? 




A. Not without a connection called the equalizer 
shown by the dotted line in the cut. 



308 eoper's catechism for 

Q. Suppose you have one machine feeding the 
bus bars and desire to connect up with it machine 
No. 2, how would you proceed ? 

A. First start up the engine Of No. 2 and turn . 
its rheostat till its pressure is the same as that of 
the bus bars or perhaps one-half volt higher. 
Then close the single-pole switch in the equalizer 
circuit, shown dotted, and finally close the ma- 
chine's double-pole switch which connects it to 
the bus bars. Its ammeter reading will then in- 
crease, and the rheostat handles of the two ma- 
chines are moved till the ammeters read alike (if 
the machines are the same size) and the voltage 
of the bus bars is correct. 

Q. Is any different arrangement of switches ever 
employed ? 

A. Yes; instead of a two-pole switch in the 
dynamo leads and a single-pole switch in the 
equalizer lead, a three-pole switch is frequently 
employed. In this case the middle blade is used 
for the equalizer wire, and is so adjusted that it 
closes the equalizer circuit just before the other 
two blades close their circuits. 

SYSTEMS OF DISTRIBUTION. 

Q. What are the two principal systems of elec- j 

trical distribution ? I 

A. The series system and the parallel system. 



STEAM ENGINEERS AND ELECTRICIANS. 309 

Q. What is the difference between the two sys- 
tems ? 



A. In the series system the entire current flows 
successively through each lamp. In the parallel 



system the current from the dynamo is divided, a 
part flowing through each lamp. Afterward these 
separate currents unite and flow back to the dy- 
namo. 

Q. What is necessary, on a series system, to 
make the lighting successful ? 

A. It must be a constant-current system — that 
is, cutting out lamps or throwing more on must 
not change the value of the current. 

Q. How is this accomplished ? 

A. By an automatic regulator on the machine 
which increases its voltage if lamps are thrown on, 
and diminishes it if lamps are cut out. 

Q. How are lamps cut out on this system ? 



310 roper's catechism for 

A. By short-circuiting them — that is, by provid- 
ing another path for the current to flow other than 
the path through the lamp mechanism and 
carbons. 

Q. What is necessary in a parallel system ? 
A. It must be a constant-potential or constant- 
pressure system. 

Q. How are lamps cut out on this system ? 
A. By interrupting the branch circuit in which 
the lamp is connected. 

Q. In the parallel system, why does cutting out 
one lamp not affect others ? 

A. Because it does not change the current flowing 
through each of the others. The current through 
any lamp depends on two things only, — the pres- 
sure and the resistance of the lamp. Turning out 
a lamp in nowise affects the resistance of other 
lamps and only affects the pressure at the terminals 
to a very slight de- 

^ j g 1^ y gree ; therefore the cur- 

Cj i <}> i 4 a i a rent flowing through 

.*^1 — o ^ 1-8 J^ the lamp is practi- 

j - j •?.... ^ cally the same as it 

() • ? T Y Y Y H* ^^^ before the other 

^— — CD I'll' — I lamp was turned off. 

Q. In the cut, what 
are the wires C A and D B called ? 
A. The feeders. 



STEAM ENGINEERS AND ELECTRICIANS. 311 

Q. And the wires E F smd G H f 

A. The mains. 

Q. And from F to the lamp and H to the lamp ? 

A. Branches. 

Q. What is the Edison three- wire system ? 

A. Two 110-volt machines are connected in 
series and the middle or neutral wire is connected 
to their junction. When the same number of 
lamps are burning on each side of the neutral wire 
there is no current flowing through the neutral 
and the same current flows through each machine. 
When No. 4 is turned out, for example, the lower 



machine supplies only the current necessary for 
lamps 5 and 6, while the upper continues to 
supply the same as before, the current for one 
lamp returning to the upper machine over the 
neutral. If all lamps on one side were turned out, 
the machine on that side would furnish no current, 
- and the other machine would continue to work as 
before. 

Q. What is the advantage of this system ? 

A. It is a 220-volt system and therefore requires 



312 



roper's catechism for 



much smaller wires to transmit a given amount 
of energy with a given loss, wdthout increasing the 
voltage of the lamps. 

Q. How much is the gain in size of wire used ? 

A. The two outside wires are just one-quarter 
as large as they would be with a 110- volt two-wire 
system. If the neutral is made of the same size, 
the three-wire system requires % as much copper 
as the two-wire system, using the same voltage 
lamps in both cases. 

TABLE 

SHOWING GAIN BY USING HIGH PEESSURES, THE SAME 
SIZE WIRES BEING USED FOR EACH CASE. 



Power 
trans- 
mitted 
in watts. 


Volts at 
which 
trans- 
mitted. 


Corre- 
sponding 
number of 
amperes. 


Power 

lost 

in 

watts. 


Volts 

drop 

in line. 


Per cent, 
power 
lost. 


Per cent, 
volts 

lost. 


CXE 


E 


C 


C^ R 


C R 


c^R^um 


CR-^E 


1100 


110 


10 


100 


10 


11. 


9.9 


1100 


220 


5 


25 


5 


2.75 


2.27 


1100 


550 


2 


4 


2 


.0227 


.363 


1100 


1100 


1 


1 


1 


.0009 


.091 



Q. If in one case, to transmit a certain power, 
we use 110 volts' pressure and in another case 
1100 volts, what will be the relative amount of 
copper used on the line ? 

A. With 1100 volts' pressure we shall need only 
Yj-g-th as much copper as with 110 volts. 



STEAM ENGINEERS AND ELECTRICIANS. 



313 



Q. What disadvantages have high jDressiires ? 

A. Greater difficulty in insulating the lines and 
danger to human life. 

Q. In proportioning the size of electrical con- 
ductors, what two requirements must be met? 

A. The wire must be large enough to transmit 
the energy without losing more than a prescribed 
per cent., and the wire must further be large 
enough so that the current will not heat it more 
than is allowed by the insurance regulations. 

INSURAI^CE EULES FOR CARRYING-CAPACITY OF WIRES. 





National 


National Board of 


Assoc. 


English 
Board of 
Trade. 


B. &S. 


Electric 


Fire Underwriters. 


Factory 


gauge. 


Light 




Mutual 




Association. 


Concealed. 


Open work. 


Ins. Co. 


0000 


175 


218 


312 


175 




000 


145 


181 


262 


145 




00 


120 


150 


220 


120 


105 





100 


125 


185 


100 


83 


1 


95 


105 


156 


85 


66 


2 


70 


88 


131 


70 


52 


3 


60 


75 


no 


60 


41 


4 


50 


63 


92 


50 


33 


5 


45 


53 


77 


45 


26 


6 


35 


45 


65 


35 


21 


7 


30 






30 


16 


8 


25 


33 


46 


25 


13 


10 


20 


25 


32 


20 


8 


12 


15 


17 


23 


15 


5 


14 


10 


12 


16 


10 


3 


16 


5 


6 


8 


5 


2 


18 




3 


5 


3 


1 



314 roper's catechism for 

Q. What is the loss of pressure allowable on 
conductors ? 

A. See '' Roper's Engineers' Handy-Book," pp. ^ 
714-717. ^ 

Q. The distance between the switchboard and 
a group of ten 16 c. p. lamps is 100 feet. What 
size wire must be used so that the loss of pressure 
on the wire between switchboard and lamp is 
only one-half of one per cent., the voltage of the 
dynamo being 110? 

A. 1. One-half of one per cent, of 110 is .55 
volt, the allowable loss of pressure. 

2. The current for ten lamps is 5 amperes. 

3. By Ohm's law C = f or i? = ^. R = '-^ 

= .11 ohm — that is, the wire must be of such 
size that the total length of it, 200 feet, has a 
resistance not exceeding .11 ohm; 1000 feet of 

this size wire would have a resistance ^r^ 

= .55. 

4. Looking in the wire tables we see that No. 7 
wire, having a resistance of .491 ohm at 60° 
Fahr. fulfils the requirement. 

5. Looking in the table of safe carrying capaci- 
ties on the preceding page, we find that according 
to the National Board of Fire Underwriters' rules 
a No. 7 wire will carry a much greater current 



STEAM ENGINEERS AND ELECTRICIANS. 



315 



PROPERTIES OF COPPER WIRE. 

ENGLISH SYSTEM — BROWN & SHAEPE GAUGE. 



2 


i'a 




Weights. 


Resistances per 1000 feet 
in International ohms. 










3 


s- 


'|2 


1000 
feet. 


Mile. 


At 60° F. 


At 75°' F. 


0000 


460. 


211600. 


641. 


3382. 


.04811 


.04966 


000 


410. 


"168100. 


509. 


2687. 


.06056 


.06251 


00 


365. • 


133225. 


403. 


2129. 


.07642 


.07887 





325. 


105625. 


320. 


1688. 


.09639 


.09948 


1 


289. 


83521. 


253. 


1335. 


.1219 


.1258 


2 


258. 


66564. 


202. 


1064. 


.1529 


.1579 


3 


229. 


52441. 


159. 


838. 


.1941 


.2004 


4 


204. 


41616. 


126. 


665. 


.2446 


.2525 


5 


182. 


33124. 


100. 


529. 


.3074 


.3172 


6 


162. 


26244. 


79. 


419. 


.3879 


.4004 


7 


144. 


20736. 


63. 


331. 


.491 


.5067 


8 


128. 


16384. 


50. 


262. 


.6214 


.6413 


9 


114. 


12996. 


39. 


208. 


.7834 


.8085 


10 


102. 


10404. 


32. 


166. 


.9785 


1.01 


11 


91. 


8281. 


25. 
20. 


132. 
105. 


1.229 


1.269 


12 


81. 


6561. 


1.552 


1.601 


13 


72. 


5184. 


15.7 


83. 


1.964 


2.027 


14 


64. 


4096. 


12.4 


65. 


2.485 


2.565 


15 


57. 


3249. 


9.8 


52. 


3.133 


3.234 


16 


51. 
45. 


2601. 
2025. 


7.9 


42. 


3.914 


4.04 


17 


6.1 


32. 


5.028 


5.189 


18 


40. 


1600. 


4.8 


25.6 


6.363 


6.567 


19 


36. 


1296. 


3.9 


20.7 


7.855 


8.108 


20 


32. 


1024. 


3.1 


16.4 


9.942 


10.26 


21 


28.5 
25.3 


812.3 


2.5 


13. 


12.53 


12.94 


22 


640.1 


1.9 


10.2 


15.9 


16.41 


23 


22.6 


510.8 


1.5 


8.2 


19.93 


20.57 


24 


20.1 


404. 


1.2 


6.5 


25.2 


26.01 


25 


17.9 


320.4 


.97 


5.1 


31.77 


32.79 


26 


1.5.9 


252.8 


.77 


4. 


40.27 


41.56 


27 


14.2 


201.6 


.61 


3.2 


50.49 


52.11 


28 


12.6 


158.8 


.48 


2.5 


64.13 


66.18 


29 


11.3 


127.7 


.39 


2. 


79.73 


82.29 


30 


10. 


100. 


.31 


1.6 


101.8 


105.1 


31 


8.9 


79.2 


.24 


1.27 


128.5 


132.7 



There are two points in this table which will be found easy to remem- 
ber and very convenient in practice— namely, that the resistance of 1000 
feet of No. 10 is almost exactly 1 ohm at 75° F., and that a change of 
t three sizes either halves or doubles the resistance, according as we go up 
or down the table. 



316 roper's catechism for 

than 5 amperes, so that a No. 7 wire is suitable 
for the requirements. 

Q. What is a mil? 

A. One-thousandth of an inch. 

Q. What are the circular mils in a wire ? 

A. The square of the diameter in mils. 

Q. What relation do the circular mileages of 
two wires bear to their resistances ? 

A. Their resistances are inversely proportional 
to their circular mileages. 

Q. A No. 2 wire, No. 4 wire, and No. 6 wire 
are connected in multiple ; to what size wire will 
their joint resistance be equal? 

A. The sum of their circular mileages is, — 
66,564 + 41,616 -f 26,244 = 134,424, and this 
is nearly the circular mileage of a No. 2/0 wire to 
which the three wires will be practically equivalent. 

WIRING AND APPLIANCES. 

Q. What two classes of wiring are there ? 

A. Open or exposed work and concealed work. 

Q. In open work, what varieties are there ? 

A. Porcelain work, where the wires are carried 
on porcelain knobs, and molding work, where the 
wires are carried in a grooved molding provided 
with a cap to hide them from view. 

Q. What are the varieties of concealed work ? 

A. Porcelain work and conduit work. 



STEAM ENGINEERS AND ELECTRICIANS. 317 

Q. What is the nature of conduit work? 

A. A system of tubes or pipes is first installed 
into which the wires are afterward drawn in. 

Q. What are the fundamental requisites for a 
conduit ? 

A. It should be strong enough to protect the 
wires from all accidents such as hammering, jar- 
ring, nails, etc. , and it should not be attacked by 
cement, plaster, or moisture. Moreover, it should 
have a smooth inside surface, so that the insulation 
of the wires may not be injured by the process of 
drawing them in. 

Q. What kind of conduits meet these require- 
ments ? 

A. An iron or steel tube like a gas-pipe has suf- 
ficient strength. If properly painted or enameled 
it is not affected by cement, plaster, or moisture. 
To secure smoothness a special pipe must be made, 
with this end in view ; or, as in some conduits, a 
lining of wood or some compound of a bituminous 
nature may be employed. 

Q. How many wires are placed in one tube? 

A. Two in the two-wire system or three in the 
three-wire system, except sometimes in the case 
of large-sized feeders where it is not possible to 
draw two in. Where alternating currents are to 
be used both the wires of a circuit must be in the 
same tube to avoid an excessive loss of pressure. 



318 



roper's catechism for 



Q. What is a cut-put, and when is it used ? 

A. A cut-out is the name given to a combination 
of fuse blocks, studs, and screws and convenient 
terminals for fastening wires. These parts are 
mounted on some insulator, as slate, marble, or 
porcelain. A cut-out with fuse is used at every 
point in a circuit where the size of wire is changed. 

Q. Why is this ? 

A. So that the fuse may protect the smaller 
wire from an excess of current. 

Q. What is a switch ? 

A. A convenient device for opening or closing 
an electric current. It performs a similar service 
to that of a valve in a water system, except that it 
has no positions corresponding to partly open. It 
must be completely open or completely shut. 

Q. What is a single-pole switch ? 

A. One which opens one wire of a circuit. 

Q. What kre double- 
pole 



-O 



and triple • 
switches ? 

A. Those which open 
two or three wires of 
the circuit. 

Q. When are three- 
way switches used ? 
A. When it is de- 
sired to control lamps from either of two points. 



3-w^y 



3 -way 



CIRCUIT WITH 3-WAY SWITCHES. 



STEAM ENGINEERS AND ELECTRICIANS. 319 

Q. In calculating the carrying capacity of 
switches, what general rules are employed ? 

A. Where current goes through solid metal 
allow one square inch per 1000 amperes, and w^here 
it goes through the joint between two pieces allow 
one square inch of contact surfaces to each 75 
amperes. 



320 roper's catechism for 



ELECTRIC LIGHTING. 

Q. In what ways may arc lamps be classified? 

A. (1) According to the kind of distribution- 
system for which they are intended, as constant 
potential arc lamps and series arc lamps; the latter 
are in general used now only by central stations. 
(2) According as they are to be supplied by direct 
or alternating current, into direct-current arcs and 
alternating arcs. (3) According to the degree of 
enclosure of the arc, into open arcs and closed arcs. 

Q. What are the requirements of all arc lamps ? 

A. All lamps to be commercially satisfactory 
must do two things: They must strike the arc — 
that is, after current has commenced to flow they 
must automatically draw the carbons apart so as 
to start the arc. They must also regulate — that is, 
as the carbons burn away they must be automat- 
ically fed together, and the feeding of one must 
not appreciably affect the brilliancy of others. 

Q. How are these accomplished in an arc lamp 
burning on a parallel or constant potential system 
of distribution? 

A. The current coming from the line to the 
positive lamp-terminal passes through a coarse 
wire coil and then through a chain or brush con- 
tact to the upper carbon, through the upper and 



STEAM ENGINEERS AND ELECTRICIANS. 321 

lower carbons, and back through a wire resistance, 
which can be varied, to the other terminal of the 
lamp and thence to line. The passage of current 
through the coil lifts an iron armature or core, as 
the case may be, to a certain distance depending 
on the strength of the current. This armature 
lifts a clutch-device which raises the upper carbon. 
The arc is thus struck and the lamp continues to 
burn, the two carbons being gradually consumed 
and the arc becoming longer. As the arc lengthens 
its resistance becomes greater and the current less. 
This allows the armature to drop down a little, 
and the clutch tripping against a stop lets the 
upper carbon slide through a little, thus shorten- 
ing the arc. The moment the arc has been 
shortened sufficiently to increase the current enough 
to lift the clutch off the tripping-stop the feeding 
of the carbon cCases ' and the lamp continues to 
burn till the arc again becomes too long. 

Q. Can two or more of these lamps be placed 
in series ? 

A. No; when several lamps are to be operated 
in series they will not all feed at the same time, so 
that the action of one would interfere with the 
others unless some different arrangements were 
introduced. 

Q. What modification of the mechanism is 
made when lamps are to be run in series ? 
21 



322 roper's catechism for 

A. An additional magnet with fine wire coil is 
connected as a shunt around the arc, and its arma- 
ture arranged so that when lifted to a certain point 
it makes the clutch feed. As the arc lengthens its 
resistance increases, and also the pressure between 
its terminals. Hence more current is sent around 
the fine wire coils, raising their armature and 
starting the feeding mechanism. 

Q. What is the difference between open and 
closed arc lamps ? 

A. An open arc lamp is one in which the air 
has free access to the arc. A closed arc lamp is 
one in which a small inner globe placed around the 
arc prevents, to a great extent, the access of air.. 

Q. What is the object of enclosing the arc? 

A. The consumption of carbon is diminished 
and the light is steadier. 

Q. How long do carbons last in the two types 
of lamp? 

A. About 7 hours in the open arc and about 
100 hours in the closed arc. 

Q. How are lamps rated commercially ? 

A. Lamps are rated in candle-power according 
to their brilliancy in the angle of greatest bril- 
liancy. Thus the ordinary street lamp rated at 
2000 candle-power gives that brilliancy only at an 
angle from the horizontal of about 45 degrees. 
At any other angle its brilliancy is less, and the 



STEAM ENGINEERS AND ELECTRICIANS. 323 

average candle-power below the horizontal will not 
be much over 800 candle-power. Such a lamp 
requires a current of 9. 6 amperes and about 45 or 
50 volts, and a lamp using such current and pres- 
sure that their product is 450 watts may be con- 
sidered commercially a 2000 candle-power lamp. 

Q. What current does a nominal 2000 candle- 
power closed arc take ? 

A. About 5 amperes on steady burning, though 
nearly double this on first starting. 

Q. What is the voltage between the carbons ? 
• A. About 80 to 90 volts. 

Q. What effect does the use of two globes have 
on the distribution of light ? 

A. It is more even with the closed arc on 
account of the two globes, but for the same reason 
a larger percentage of light is absorbed. 

Q. What are the essential features of the incan- 
descent lamp ? 

A. Incandescent lamps consist of a carbon 
filament attached to platinum wires, which is 
mounted in a glass globe from which the air has 
been exhausted and which is sealed up so as to ex- 
clude air. The platinum wires serve to connect 
the filament to the terminals of the lamp base. 
The vacuum is made as perfect as possible, so that 
there may remain no air inside the globe in which 
the highly heated filament would burn aw^ay. 



324 roper's catechism for 

Q. How is the filament made ? 

A. By taking a slender piece of some material 
consisting largely of carbon, such as bamboo, silk, 
paper, or cellulose, and heating it intensely in a 
furnace so as to drive out all the other material, 
leaving a very nearly pure carbon thread. In 
order to smooth out the roughness and make its 
section uniform at all points, a current is passed 
through it large enough to heat it to nearly a white 
heat in an atmosphere of some hydrocarbon, like 
coal gas. This causes carbon to be deposited most 
largely at the hottest points, which are those of 
the smallest cross-section. The filament is then 
attached to the platinum leading-in wires and 
placed in the globe. 

Q. What is the remainder of the process of 
making the lamp ? 

A. A mechanical air-pump exhausts the air 
from the globe, and, finally, by passing a strong 
current through the filament, the latter, heated to 
incandescence, burns away the remnant of oxygen 
remaining. The bulb is then sealed up and the 
platinum wires connected to the lamp-base ter- 
minals. Finally, the lamps are tested to see at 
what voltage they will give the candle-power for 
which they are intended. 

Q. What is the effect of use on the lamp ? 

A. Its candle-power graduall}^ diminishes owing 



STEAM ENGINEERS AND ELECTRICIANS. 325 

to the deposition of carbon from the filament on the 
walls of the globe, the layer of carbon absorbing 
the light-rays, so that after a few hmidred hours' 
burning the lamp must be replaced by a new one. 

Q. What candle-powers are ordinarily made ? 

A. 8, 10, 12, 16, 20, 24, 32, 50, 100, 150, 
though the last two sizes are rarely used, arc lamps 
being employed instead. 

Q. What are the voltages commonly made ? 

A. From 50 to 60, 70 to 80, 100 to 120, and 
200 to 250 lamps of 110 and thereabouts being 
the most common. 

Q. Why are 220-volt lamps employed ? 

A. To secure economy in the size of the dis- 
tributing wires. 

Q. Why are they not more extensively used ? 

A. Because they are inferior in quality to the 
lower voltage lamps. 

Q. What are the two important qualities of an 
incandescent lamp ? 

A. Its length of life and its efficiency. 

Q. What is meant by efficiency ? 

A. The number of watts power which must be 
supplied to the filament to produce 1 candle-power. 
The most efficient lamp is that one which produces 
1 candle-power with the least number of watts. 

Q. Is there any relation between life and effi- 
ciency ? 



326 



roper's catechism for 



A. Yes; a somewhat unfortunate one, since we 
cannot improve one without injuring the other. 
The efficiency increases with the temperature of 
the filament, while the life is correspondingly 
diminished. 

TABLE 

OF EFFICIENCIES AND LIFE OF INCANDESCENT LAMPS. 



Efficiency. 
Watts per can- 
dle. 


Life-hours. 


Watts per 16 
c. p. lamp. 


Amperes for 16 

c. p. 110-volt 

lamp. 


2.6 
3.1 
3.6 
4.0 


400 

600 

800 

1000 


41.8 
49 6 
57.6 
64.0 


.38 
.45 
.52 
.60 



Q. When is it desirable to use a low and when 
a high efficiency lamp ? 

A. It depends upon the cost of power. If coal 
is cheap, it pays to use a low efficiency and long 
life. If coal is dear, the high efficiency lamp 
should be used, provided the speed regulation of 
the engine is good enough to prevent fluctuations 
in the voltage of the dynamo, it being understood 
that any rise in voltage above that for which the 
lamp is intended shortens its life very seriously. 
Of course, where all the exhaust steam of the 
generator engine is used in steam heating it is de- 
sirable to use the low efficiency and long-life lamps. 



STEAM ENGINEERS AND ELECTRICIANS. 327 



ELECTRIC MOTORS* 

Q. How does a motor differ from a dynamo, as 
regards the purpose for which it is used ? 

A. A dynamo transforms mechanical energy 
into electrical energy. A motor transforms elec- 
trical energy into mechanical energy. 

Q. How do direct-current motors differ from 
dynamos, as regards construction ? 

A. Practically any direct-current dynamo, if 
current be supplied to it, will operate as a motor, 
and a well-designed dynamo will make a good 
motor. Certain alterations in winding and in 
other details are made in motors to improve cer- 
tain qualities that may be specially desired. 

Q. Will a dynamo used as a motor run in the 
same direction that it had as dynamo ? 

A. A series dynamo, when used as a motor, will 
run in the opposite direction, and a shunt motor 
will run in the same direction. 

Q, What must be done to reverse the direction 
in which a motor will run ? 

A. Change the connections so as to reverse the 
direction of current through either (but not both) 
field or armature. It may further be necessary 
to shift the brushes to prevent sparking. 

Q. When are series motors employed? 



328 ROPER'S CATECHISM FOR 

A. The series motor is used where it is necessary 
to start with full load and where automatic regu- 
lation for constant speed is not necessary, a hand 
regulation being used, as, for example, in hoists, 
cranes, street railways, etc. 

Q. When are shunt motors used ? 

A. A shunt motor is used where automatic 
regulation for constant speed is desired. A good 
shunt motor will not change its speed more than 
5 per cent, when the load is varied from zero to a 
maximum. 

Q. Under what circumstances would compound 
motors be desirable ? 

A. Compound motors are used where closer 
speed regulation than that given by shunt motors 
is desired, and in special cases, such as on planers 
where it is desired to check the sudden large flow 
of current during reversal. 

Q. With a series motor, whose use is almost 
entirely on constant pressure circuits, how is 
regulation of speed accomplished ? 

A. There are two common methods: 

1. To change the pressure supplied to it, by 
putting in series with the motor a rheostat in 
which more or less pressure is used up according 
to the position of the rheostat-handle. Lowering 
the pressure will, of course, lower the speed. 

2. To change the strength of the field of the 



STEAM ENGINEERS AND ELECTRICIANS. 329 

motor. This is done by winding the field coils in 
sections and bringing out the ends to a sort of 
commutating device called a controller. In one 
position of the controller handle the sections will 
all be in series, cutting down the current and 
making the ampere turns of the field, and hence 
its strength, low. In the next position, for ex- 
ample, three sections will be in series and three 
others in series, and the two sets of three in 
multiple, which will diminish the resistance, let 
more current through, and increase the ampere 
turns. Another position will put more in multiple 
and less in series, and so on till the final step puts 
all the sections in multiple, giving the lowest 
possible resistance, highest number of amperes, 
greatest number of ampere turns, and strongest 
field. With the series motor on constant potential 
circuits the speed is increased in proportion as we 
increase the field strength. A combination of the 
two methods is frequently used, the resistance 
being used during the first positions in order to 
cut down the excessive flow of current on starting. 

Q. How are shunt motors, on constant pressure 
circuits, regulated for changes in speed ? 

A. By putting resistance coils in series wdth the 
armature and throwing more or less of them in 
according as we want lower or higher speed. 
Another method is to put a rheostat in the field 



330 roper's catechism for 

circuit and vary the current flowing around the 
field coils by means of it. 

Q. What effect does weakening the field have 
on the speed of the series motor on constant pres- 
sure circuits ? 

A. It lowers the speed. 

Q. What is the effect with a shunt machine ? 

A. Weakening the field increases the speed. 

Q. How are compound motors regulated ? 

A. Generally like shunt motors; but in some 
special cases the series coils are wound in sections 
and thrown in series, and finally in multiple, as 
is the case with series motors. 

Q. In starting shunt or compound motors what 
precaution is necessary ? 

A. It is necessary to put a considerable resist- 
ance in series with the armature, on account of its 
very low resistance, which will vary from y^Q- to 
YQ^o-g- of an ohm or less, according to its size. 
Such a low resistance thrown across 110 volts 
would cause an enormous current, which would 
injure the commutator and brushes by sparking 
and the armature coils by heating. As the 
machine speeds up the resistance may be cut down, 
because the armature, which is turning in a mag- 
netic field, produces an electro-motive force oppo- 
site to that of the circuit, which tends to cut the 
current down. 



STEAM ENGINEERS AND ELECTRICIANS. 331 

Q. What further protective devices are needed 
with motors ? 

A. All motors need to be protected from the 
danger of being overloaded. An overload, by 
slowing down the motor, diminishes the back 
electro-motive force and therefore allows an excess- 
ive current to flow, which, if long continued, 
would burn out the armature. The protection 
formerly used was a pair of fuses, one in each of the 
circuit wires, which were of such a size that they 
were expected to blow at any current exceeding 
that corresponding to the maximum load for which 
the motor was designed. Owing to the uncertain 
action of fuses, a circ ait-breaker is now almost 
universally used, mounted on the starting-box. 
Another thing which must be guarded against is 
this: Suppose that' the circuit to which the motor 
is connected is overloaded, perhaps by some 
accident, and the circuit-breaker of that circuit 
on the switchboard should open. This would 
cut off current from the motor and it would 
stop. Now if nothing were done except at the 
switchboard to throw in the circuit-breaker 
again, we should throw the full voltage on the 
motor armature, none of the rheostat being in 
series with it, as it had been previously cut out of 
the circuit when the motor was first brought up to 
The result, of course, Avould be a tre- 



332 roper's catechism for 

mendous flow of current and injury to commu- 
tator, brushes, and perhaps the armature, depend- 
ing upon how quickly some one opened the switch 
which connected the motor to the circuit. To 
obviate this difficulty, the rheostat arm has 
attached to it a spring which tends to pull it back 
to the position in which all of its coils are in 
series with the armature. At the other limit of 
its motion, where it would stand when all the 
coils had been cut out of the circuit, is a magnet 
wound with fine wire and supplied from the 
circuit wires. When the rheostat arm gets to this 
position the magnet holds it there by its attraction 
for a piece of iron mounted on the arm, as long 
as the current flows through the coil; but if the 
circuit-breaker goes off or the voltage disappears 
for any reason, the magnet lets go and the spring 
pulls the rheostat arm back to the position of safety. 

Q. What are the commercial sizes in which 
motors are built? 

^. A, *, i, h 1, 2, 3, 5, 71 10, 15, 20, 25, 50, 
75, 100, and upward. 

Q. What are the standard voltages ? 

A. 110 to 125, 220 to 250, and 500 to 550. 

Q. What is a motor- generator ? 

A. A combination of motor and generator on 
the same shaft. The most easily understood form 
would be a motor which might be designed for any 



STEAM ENGINEERS AND ELECTRICIANS. 333 

voltage, speed, and power, coupled directly to the 
shaft of a dynamo designed for the same speed, 
but for any voltage and the same output as the 
motor. Such a machine has two distinct com- 
mutators, brushes, armatures, and fields. 

Q. How is this arrangement modified in prac- 
tice? 

A. By using a common armature core and field, 
and putting the two sets of armature windings on 
the same core, insulated, of course, carefully from 
each other. 

Q. What are some of its principal uses ? 

A. 1. To change from a high pressure and small 
current to a lower pressure and correspondingly 
greater current. 

2. With its generator armature in series with 
some circuit to raise the pressure of that particular 
circuit higher than that of the other circuits sup- 
plied from the principal generator. In such uses 
it is called a booster. 

3. In connection with storage batteries, it being 
used in series with the charging mains to increase 
the pressure in proportion as the batteries become 
more fully charged. 

It is also used to a considerable extent in tele- 
phone exchanges for operating the calling circuits, 
the generator end being arranged to give an alter- 
nating current. 



334 roper's catechism for 



STORAGE OR SECONDARY BATTERIES. 

Q. Of what does the storage battery, as com- 
mercially sold, consist? 

A. Of two lead plates, or sets of plates, im- 
mersed in a jar containing dilute sulphuric acid, 
the plates having the form of grids, the holes in 
which are filled with active material. 

Q. Of what does this active material consist ? 

A. On the positive plate, of peroxide of lead. 
On the negative plate, of metallic lead in finely 
divided, spongy condition. 

Q. What do you mean by the positive plate ? 

A. Just as with any battery, the plate from 
which current will flow through a conductor con- 
necting it to the other plate. 

Q. How can you tell by the eye which is the 
positive plate of a storage cell ? 

A. By its reddish color. 

Q. Is there any other way ? 

A. Yes; there is always one more negative plate 
in a cell than there are positive plates. 

Q. Are the positive and negative plates in con- 
tact? 

A. The positives are all joined to each other, 
likewise the negatives; but the positives are 
separated from the negatives by about ^ of an 



STEAM ENGINEERS AND ELECTRICIANS. 335 

inch, the space between bemg filled with sulphuric 
acid. 

Q. What do you mean by the discharge of a 
cell? 

A. Allowing it to furnish current, as it will do 
if the positive and negative terminals are con- 
nected by a conductor. 

Q. What are, roughly, the chemical changes that 
take place during discharge ? 

A. The peroxide on the positive is changed to 
lead sulphate. The spongy lead on the negative 
is likewise changed to lead sulphate. 

Q. What do you mean by charging a cell ? 

A: Running a current from some generator 
through the cell in the opposite direction to that 
of the current which it furnished during dis- 
charge. 

Q. What chemical action takes place ? 

A. The reverse of what occurred during dis- 
charge. On the positive plates lead sulphate is 
changed to lead peroxide and on the negatives to 
metallic lead. 

Q. What pressure is furnished by such a storage 
cell? 

A. When fulty charged, about 2.2 volts. This 
gradually diminishes during discharge to 1.<S volts 
beyond which point further discharge would injure 
the cell. 



336 roper's catechism for 

Q. What are the principal sources of trouble, 
and how are they remedied? 

A. The principal troubles of storage cells are 
short-circuiting, buckling, and sulphating. The first 
is caused by buckling of plates or by the dropping 
out of portions of the pencils of active material, 
which in time form between the positive and 
negative plates a connection which causes loss of 
charge and destruction of the plates if not noticed 
and remedied by taking out the material. Buck- 
ling is due to an excessive rate of discharge or an 
unequal discharge at different parts of the plate. 
To assist in preventing it the plates are separated 
by glass or rubber distance-pieces. Sulphating, 
or the production of a complex, hard, white lead 
sulphate, is caused by carrying the discharge of 
the battery too far or by letting it stand too long 
without recharging. It is remedied by persistent 
charging. 

Q. What are the principal advantages of using 
storage cells ? 

A. To take care of light loads, thus permitting 
dynamos, engines, and perhaps a boiler to be shut 
down; to maintain a steady pressure; and to take 
care of the ' ' peak of the load, ' ' * thus enabling 
the machinery to work at a more even load and 
securing greater economy. 

*See "Roper's Engineers' Handy-Book," page 755. 



STEAM ENGINEERS AND ELECTRICIANS. 66 i 

Q. How are storage cells rated ? 

A. By their capacity in ampere-hours. Thus, a 
cell of 50 ampere-hours is one which when dis- 
charged at its normal rate gives out such a number 
of amperes for such a number of hours that the 
product of the number of amperes by the number 
of hours equals 50. The capacity of a cell, or the 
number of ampere-hours which can be taken from 
it without carrying the voltage lower than 1.8 volts, 
is very much affected by the rate of discharge, 
being much less at a rapid than at a slow rate of 
discharge. 

Q. What is the efficiency of a storage cell, and 
how is it measured ? 

A. The efficiency of a cell is the ratio between 
the amount of power which can be taken out of 
it and that which is put into it. It, like capacity, 
varies with the rate of discharge, and may be 
anywhere from 50 to 95 per cent., according to 
the charge and discharge rates used. Eighty per 
cent, for the normal discharge-rate of a cell is a 
good value except for the very largest cells. To 
measure the efficiency the watt-hours put in dur- 
ing charge are measured by an ammeter and volt- 
meter, and, similarly, the watt-hours taken out in 
discharge. The quotient of the latter by the 
former is the efficiency. 



22 



338 roper's catechism for 

METHOD OF CONNECTING STORAGE BATTERIES. 

Owing to the fact that the electro-motive force 
of a cell increases with charge and diminishes with 
discharge, it is necessary to have special arrange- 
ments by which a dynamo while supplying hghts 
may charge a battery of cells, and by which the 
electro-motive force of a set of cells may be kept 
constant while they are supplying lamps. The 
arrangement for discharge will be first described. 
Supposing a 110-volt system, we must have a 
number of cells in series equal to \-^^ volts, or 
about 60 cells. When fully charged, as each cell 
has an electro-motive force of 2.2 volts, the total 
electro-motive force of the 60 cells would be 132 
volts, a pressure which would seriously injure the 
lamps. When the cells are fully charged, there- 
fore, a sufficient number are switched out of cir- 
cuit to bring the pressure down to 110 volts. As 
the cells discharge and their electro-motive force 
falls, these cells are switched back into the circuit 
one at a time, till at the end of the discharge they 
are all in circuit. 

In charging, the electro-motive force rises. As 
it is desired to run 110-volt lamps and charge the 
cells at the same time, we cannot raise the pres- 
sure of the lighting dynamo; so an auxiliary 
dynamo or booster is employed, its armature being 



STEAM ENGINEERS AND ELECTRICIANS. 



339 



put in series with the cells and its field varied by 
its rheostat so as to give enough additional volts 
for charging at the proper rate. The accompany- 




ing diagram of connections shows the arrange- 
ment. B is the booster and R its rheostat. V is 
a voltmeter and A an ammeter, so arranged that 



340 roper's catechism for i 

■i 
its needle stands in the center of the scale when no '■ 
current is flowing through it, moving to one side 
for a charging current and to the opposite side for a 
discharge current. K represents the main battery 
and H the switch which throws the reserve cells 
in and out. >S is a double-throw switch, which in 
one position connects the batteries to the lamp to 
be supplied with current, and in the other position 
connects it to the dynamo for charging. E is sl 
switch for connecting the voltmeter, so as to give 
the voltage of the battery, the line, and the charg- 
ing dynamo and booster respectively. is an 
automatic circuit-breaker, which will operate if 
too great current is taken out of the batteries, and 
C is a circuit-breaker which will open the circuit 
if the charging current becomes less than a certain 
value. This last is necessary if a compound- 
wound dynamo is used in order to protect the 
dynamo from having a reverse current sent through 
it from the battery if by accident it was slowed 
down or stopped before the charging switch had 
been opened. 

Several other arrangements are employed ; but 
a proper understanding of the one described above 
will be sufficient to enable the engineer to com- 
prehend the others without difficulty. 



STEAM ENGINEERS AND ELECTRICIANS. 341 



ELECTRIC SIGNALS. 

Q. Of what four elements are most signal 
systems made up ? 

A. Of the battery, line, the operating station, 
and the receiving mechanism. 

Q. What is the function of each element ? 

A. The battery furnishes the electrical energy 
for operating the signals, and the line serves to 
transmit this energy. The operating station, which 
generally consists of a key, a switch, or a push- 
button, closes the electrical circuit and permits 
the operating current to flow. The receiving sta- 
tions are somewhat varied in design. They may 
consist of a bell or telegraph sounder, giving the 
signals by sound, or of a galvanometer or a shutter- 
drop, which conveys the signals by means of 
sight. Frequently the two methods of sound and 
sight are combined. 

Q. Of what does an electric bell consist ? 

A. Of an electro-magnet, to the armature of 
which is connected a hammer arranged to strike a 
gong when the armature is pulled up to the core 
of the magnet by the passage of an electric cur- 
rent. When current ceases the magnet loses its 
strength and a spring pulls the armature away 
from the core and also the hammer from the gong. 



342 



roper's catechism for 



Q. Into what classes are bells divided ? 
A. Into single-stroke bells, which make but one 
stroke each time that circuit is closed, and vibrat- 
ing bells, whose hammer continues to vibrate as 
long as circuit is closed. 

Q. How is a single-stroke bell 
connected ? 

A. As shown by the solid 
lines in the cut. 

Q. How is a vibrating bell 
connected ? 

A. As shown in the cut, the 
connection F-D being considered 
as removed. 

Q. Explain the complete ac- 
tion of the vibrating bell. 
A. When the button is pressed down, the cir- 
cuit being closed, current will flow from F to B, 
B to the contact point C, through the armature 
E to D, from D through the magnet coil to A, 
and from A back through the closed push and 
battery to F. Owing to the current, the electro- 
magnet pulls the armature E toward itself and 
the hammer strikes the gong G; but as soon as 
the armature moves toward the magnet the circuit 
is opened, because C no longer touches E. The 
current therefore stops, and as the electro- magnet 
no longer has any strength the armature is pulled 




STEAM ENGINEERS AND ELECTRICIANS. 343 

away from it by the spring S. This movement, 
however, brings E and C into contact again, caus- 
ing the whole action to be repeated, and this con- 
tinues as long as the push-button is held down, 
provided the battery keeps up its strength. 

Q. What three styles of bells are there ? 

A. Wooden box, the working parts of which are 
covered with wood ; iron box, when they are cov- 
ered with iron, and skeleton frame, w^hen they are 
not covered at all. 

Q. Show how you would connect three bells to 
ring by one push-button. 
t A. 

[T o[::jio[:{iO[] 



Q. Show how to connect two bells to be rung 
by either of two pushes. 
' A. 






41' 



d od 



Q. Show how you would connect a return call 
between two points. 



844 roper's catechism for 

A. 



□O 



ill- 



d 




Q. What is an annunciator ? 

A. The annunciator in principle consists of a 
number of bells mounted together in a case, each 
operated by its own push located in some distant 
place. In practice, however, it would be difficult 
to tell from the sound of the bells which station 
was calling, so the hammers and gongs are 
omitted, and instead we have a simple mechanism 
operated by the armature, called the drop. 

Q. Explain the details of one form of drop. 

A. It consists of a coil whose armature is an 
iron rod which is sucked up into the coil when 
current passes through it. This releases a pivoted 
needle, which is hung eccentrically so that it turns 
from the horizontal to the vertical position. Each 
needle being numbered or otherwise marked the 
point from which the signal was sent is, of course, 
known. 

Q. How are the needles restored ? 

A. By a rod carrying little stops, which when 
pushed up force the needles back to their original 
position. 



STEAM ENGINEERS AND ELECTRICIANS. 



345 



Q. What is an automatic set-back annunciator ? 

A. One in which this rod is lifted by an electro- 
magnet so connected that current flows through it 
when any push-button is pressed. All the needles 
are pushed back to their horizontal position, after 
which the needle corresponding to the push-button 
last pressed turns to the vertical position. 

Q. Show by a diagram the connections for an 
automatic set-back annunciator system. 

A. 




Signal Bell. 



Q. How does the return-call annunciator system 
differ from this ? 

A. By the addition of another wire between 
each push-button and the annunciator. 

Q. What is a fire-alarm attachment ? 

A. A device, frequently added to annunciators 
for use in hotels, which closes the circuit of the 



346 roper's catechism for 

bells in the rooms, the effect being the same as if 
all the return- call pushes on the instrument were 
pressed simultaneously. 

Q. How does a burglar-alarm system differ 
from the ordinary annunciator system ? 

A. Burglar- alarm systems are similar to simple 
annunciator systems, with the addition of a bell 
in an auxiliary circuit which is closed when any 
of the drops operate. This auxiliary bell will 
therefore continue to ring till some one comes 
along and restores the drops to their usual posi- 
tion with the needles horizontal. The push- 
buttons are of a somewhat modified pattern and 
are placed in doors and window-casings, so that 
if either a door or window is opened the contacts 
of the button touch each other and close the 
circuit, causing the corresponding drop on the 
instrument to operate. Frequently the pushes of 
all the windows and outside doors of any one 
room are connected in multiple on one circuit, so 
that any one of them when closed operates the 
drop corresponding, it not being necessary to 
have a drop for each window and door, but only 
for each room. 

Q. Why are watchmen's clock systems used? 

A. To insure that watchmen make their rounds 
at the time and in the order that they are expected 
to do so. 



STEAM ENGINEERS AND ELECTRICIANS. 347 

Q. Into what classes may they be divided ? 

A. Into the battery and magneto systems, ac- 
cording as the energy for actuating the recording 
device is obtained from a battery or from a small 
dynamo. 

Q. Explain the arrangement and operation of a 
battery system. 

A. This system is wired like a simple annun- 
ciator system. Its push-buttons are of such 
pattern that circuit will be closed in them only 
by pushing into them a special key carried by 
the watchman. The annunciator of the ordinary 
system, with slight modification, becomes the 
watchman' s clock, the signal bell and self-restoring 
magnet of the annunciator being omitted. The 
armature of each drop is made to actuate a little 
needle which punctures a hole in a paper recording 
dial. This dial being divided in spaces corre- 
sponding to the hours from 12 o'clock to 12 o'clock, 
and being further subdivided into spaces corre- 
sponding to five minutes, and rotating so as to make 
one complete turn in the 12 hours, the position of 
the punctured holes on the paper tells at what time 
they were made by the watchman. The dial has 
also a number of circles marked on it correspond- 
ing to the number of stations, and each needle 
pricks its holes in one of the circular spaces 
formed by these rings, so that a hole in a certain 



848 roper's catechism for 

ring means that the ke}^ has been put in the cor- 
responding station push-button. 

Q. What is the weak point of this system ? 

A. That if the watchman can get at the two 
wires leading to any station and can connect them 
together, he can make the clock register as if he 
had actually gone to that station. 

Q. How does the magneto system differ from it ? 

A. The wiring, and clock are the same; but 
instead of the special push-button to be operated 
by a key, a little dynamo, called a magneto, is 
placed at each station. The watchman carries a 
handle which he puts on a stud connected with 
the shaft of the dynamo armature. Turning the 
handle sends a current through the coil corres- 
ponding at the clock and causes the needle to 
make a record. 

Q. What are the advantages of the magneto 
system ? 

A. There are no batteries to be taken care of 
and the watchman practically cannot make a 
proper record without going to the station. 

Q. What kind of batteries are used for operating 
the above systems ? 

A. Some form of the zinc-carbon sal-ammoniac 
cell. 

Q. How many are required for the different 
systems ? 



STEAM ENGINEERS AND ELECTRICIANS. 349 

A. For single bells or annunciators with short 
circuits, as in a dwelling-house, three cells are 
usually sufficient. For larger buildings five or 
six will be needed. For automatic fire-alarms a 
much larger number is needed, the exact number 
being stated by the manufacturer, as a rule. For 
burglar- alarm and watch -clock systems six are, as 
a rule, sufficient, and sometimes a less number 
may be used. 



350 



ROPER'S CATECHISM FOR 



THE TELEPHONE. 

The phenomenon of sound is caused by vibra- 
tions of the particles of air; its pitch is dependent 
upon the number of vibrations per second, its 
loudness on the wideness of those vibrations, and 
its quality, that property by which we distinguish 
tones of the same pitch and loudness, upon the 
form of the vibrations. This last point is some- 




what difficult to understand. Suppose that a 
mass of air is set in vibration by a tuning-fork, 
and that we study the motion of a single particle 
of air by plotting on a flat surface. Let distances 
to the right of the vertical represent time, and 
vertical distances represent the distance which the 
particle has moved through at any time. The 
motion of the particle would be represented by the 
wavy line in the figure. Distances above the 



STEAM ENGJNEERS AND ELECTRICIANS. 351 

horizontal correspond to motion in one direction 
from its position of rest, and distances below the* 
horizontal represent, similarly, motion in the oppo- 
site direction. If we set the air into vibration by 
means of a bowed violin- string, the shape of the 
wavy line would be very much altered, as in the 
second figure. To perfectl}^ reproduce sounds it is 
necessary to reproduce the pitch or number of 
waves per second and the quahty or form of these 
waves, and sufficient wideness of vibration to 
affect the Hstening ear. 

The telephonic transmission of speech between 
two points may be best considered in two parts: 
(1) The transmitter, which produces in the wires 
connecting the two points a varying current 
whose curve of variation, if plotted, has the same 
number of vibrations per second, and whose form 
is the same as that of the sound-waves which 
strike upon the diaphragm of the transmitter 
mouthpiece. (2) The receiver, into which comes 
this varying current, which is made to set a dia- 
phragm into vibrations exactly similar to those of 
the transmitter diaphragm. The receiver dia- 
phragm, of course, sets the air surrounding it into 
vibrations similar to those caused by the voice 
speaking, and the ear of the listener is affected in 
the same way, though not so strongly as if the 
speaker were talking directly to him. 



352 roper's catechism for 

Q. Describe the magneto receiver. 

A. The magneto receiver consists of a bar mag- 
net with a short cylindrical pole-piece of soft iron 
on one end. Mounted on this pole-piece as an 
axis is a little wooden spool wound with fine wire. 
In front of the spool is a thin circular disk of soft 
iron. 

Q. What improvements have been made in the 
receiver ? 

A. It is now made with a magnet of horse-shoe 
pattern, each pole having a spool of wire on it. 

Q. What was the original form of the trans- 
mitter ? 

A. Originally the same instrument was used 
alternately as transmitter and receiver. 

Q. Explain the operation when two of these 
receivers are connected together by two wires, one 
being spoken into and the other serving as a 
receiver. 

A. The voice of the speaker sets the diaphragm 
of the transmitter into vibration. The motion of 
the iron near the magnet-pole alters the position 
and density of the magnetic lines of force enclosed 
by the coil and sets up a varying electro-motive 
force in the coil. This produces a current in the 
line with a variation or wave-form similar to the 
original sound-wave. This varying current flow- 
ing around the coil of the receiver causes the 



STEAM ENGINEERS AND ELECTRICIANS. 353 

strength of its pull on the receiver diaphragm to 
vary in a similar way, and therefore to set up in 
the receiver diaphragm vibrations similar to those 
of the transmitter diaphragm. This sets the 
surrounding air into similar vibration. This 
causes the listener's ear to be affected just as if 
the speaker were talking directly in his ear, 
although not so loudly. 

Q. What form of transmitter is now used ? 

A. That which is known as the battery or car- 
bon transmitter. 

Q. Explain how it differs from the magneto 
transmitter. 

A. In the magneto transmitter just described 
the varying current is produced by setting up an 
electro-motive force whose wave-form of variation 
is similar to that of the sound-wave producing 



^ 



H' 



y^ 



CARBON TRANSMITTER AND CIRCUIT. 

it. Another way to produce the varying current 
is to use a constant electro-motive force^- but 
employing a resistance varied by the sound-wave 
and having the same wave-form of variation. A 
current is sent through the circuit consisting of 
23 



354 roper's catechism for 

the receiver, line, and carbon contact, as shown 
in the diagram. One of the carbon pieces is fixed 
and the other moves with the diaphragm. When 
the latter is spoken against, its vibrations cause 
the varying pressures on the contact between the 
two carbon pieces. This causes the varying resist- 
ance, which produces the varying current neces- 
sary to transmit speech. 

Q. Do the present forms of transmitter consist 
of a single carbon contact ? 

A. No; in order to make the variation of resist- 
ance as great as possible the number of contacts 
is increased by having the circuit pass through a 
number of small carbon particles against which 
the diaphragm presses. 

Q. What is the induction coil, and why is it 
used ? 

A. On long lines the resistance of the lines, 
which is fixed in value, is so much greater than 
that of the variable carbon contacts that the effect 
of the latter in varying the total resistance in cir- 
cuit is practically zero. To overcome this diffi- 
culty the induction-coil is used. Jt consists of a 
bundle of fine iron wires about three inches long, 
and wound around these as an axis is a coarse 
wire coil of about No. 16 wire and a fine wire 
coil of No. 24 or smaller, according to the length 
of line. 



STEAM ENGINEEES AND ELECTRICIANS. 355 

Q, How is the coil connected ? 
I A. As shown in the diagram. 

11=3=^ pC=B 

IaaaaAa4 /^AA/^AAJ 






CONNECTIONS USING INDUCTION COILS. 

Q. What are the methods used in calUng up ? 

A. By a battery and ordinary vibrating bell, 
called the battery call, and by a magneto and special 
bell, called the magneto call. 

Q. When is the former used ? 

A. Generally for distances not exceeding a few 
hundred feet. 

Q. On what two systems are telephones oper- 
ated? 

A. On the intercommunicating system and on 
the exchange system. 

Q. What is the intercommunicating system ? 

A. The intercommunicating system consists of 
instruments as above described, combined with a 
suitable number of wires running to all instru- 
ments, and at each instrument such a form of 
mechanical-contact changing switch as to enable 
each telephone station to call up any particular 



356 eoper's catechism for 

station without interfering with any others who 
may be talking. 

Q. What is the general scheme of wiring for 
this system? 

A. To each instrument as many wires are run 
as there are telephones in the system, plus two 
(three in some systems). These wires are prefer- 
ably of different colors, to facilitate making proper 
connection. 

Q. What kind of a call is used ? 

A. Either may be employed, but the battery 
call is more common. 

Q. What requirement must a successful inter- 
communicating system fulfil ? 

A. That no other act is necessary after finishing 
conversation than to hang up the receiver on the 
hook. Some systems require that a lever shall be 
returned to a certain point or that a plug shall be 
put in a certain hole in addition to hanging up 
the receiver. Such systems are faulty. 

Q. How many instruments are used on such 
systems ? 

A. Any number may be used, but it is rarely 
advisable to go above twelve or fifteen, the 
exchange system being preferable when a greater 
number is required. 

Q. What is the general nature of exchange 
systems ? 



STEAM ENGINEERS AND ELECTRICIANS. 357 

A. In such systems two (or sometimes three) 
wires run from each telephone to a central point, 
at which an operator sits, whose duty it is to con- 
nect the lines of any two telephones by means of 
a convenient switchboard and to disconnect them 
when they have finished talking. The connections 
are made through a pair of flexible cords, called 
talking-cords, which are attached to plug-shaped 
pieces. 

Q. How are the subscribers called up ? 

A. By either battery or magneto call. 

Q. What is the general method of operation in 
an exchange system when one party wishes to talk 
to another ? 

A. See ''Roper's Engineers' Handy-Book," 
pages 771-773. 

Q. May any number of instruments be con- 
nected on an exchange system ? 

A. Yes; the switchboard is increased as fast as 
the addition of instruments renders it necessary. 



J 



INDEX. 



Absolute zero of temperature, 38 
Acceleration, definition of, 4 

relation between mass, force, 
and, 7 
Accumulators, electric {see Storage 

Batteries) . 
Air, 50 

compressors, 26 

flow of, 27 

motors, 28 

volume of, at various tempera- 
tures, 53 
Alloys, 243 

Alternating currents, 298 
Altitude measured by barometer, 55 

by thermometer, 55 
Ampere, 268 

Angle of advance or angular ad- 
vance, 201 
Annunciator, electric, 344 
Anode. 249 
Arc lamps, 320 
Armatures of dynamos, 299 
Atmosphere, 52 
Atmospheric pressure, 52 
Atomic weights, 237 
Atoms and molecules, 237 
Automatic cut-otf and throttling 
engines, comparison of, 195 

engines {see Engines). 

stoking of boilers, 165 
Axle, the wheel and, 16 . 



Babcock & Wilcox boilers, 84 
Barometer, 54 
Beams, 246 

uniformly loaded, 247 
Bearings {see Journals). 
Bells, electric, 341 
Belting, 20 

Belts, calculation of width, 20 
Boiler chimneys and stacks, 167 

compounds, 123 

flues, 160 



Boiler furnaces, 160 

grates, 163 

materials, 98 

thickness of, 99 

setting, 109 
Boilers, 69 

automatic stoking of, 165 

Babcock & Wilcox, 84 

care and management of. 111 

Cornish, 77 

cylindrical, 75 

tire-tube, 80 

firing of. 111 

Galloway, 80 

grate surface per horse-power 
of, 95 

importance of correct supply 
of air to, 141 

Lancashire, 79 

locomotive, 89 

marine, 87 

priming of, 125 

rating of, 91 

return tubular, 83 

riveted joints of, 100 

scale and corrosion in, 123 

tubular, 81 

water-tube, 84 
Boiling-point of water, 58 
Bourdon steam gauge, 138 
Brass, 243 
Bronze, 243 
Burglar alarm, 346 
Bus-bars on electric switchboards, 



Calorific value of coals, 48 
Carbon effect on strength of steel, 

241 
Cards, indicator {see Indicators). 
Cast-iron (see Iron). 
Cathode, 249 

Centennial rating of boilers, 92 
Centigrade thermometer scale, 38 
Chemical elements, 236 



359 



360 



Chimneys. 167 

Circuit breakers, 305 

Clutches, friction, 24 

Coal, 45, 47 

Coke, 47 

Collapsing pressure of boiler flues, 

rule for, 161 
Columns, 247 
Combustibles, relative value of, 

48 
Combustion, 44 

heat of, 48 
Commutators of dynamos, 298 
Composition of forces, 11 
Compound dynamos, 30 

engines, 191, 192 
Compressed air, flow of, through 

pipes, 28 
Compression in engines, 225 
Compressors, air, 26 
Condensers, 233 

injection water required, 234 

vacuum of, 234 
Condensing engines, economy of, 

188 
Conducting power of substances for 

heat, 42 
Conduction of heat, 42 
Conductivity, electrical, 270 
Conductors, electrical, 272, 274 
Conservation of energy, 10 
Convection of heat, 42 
Copper, 242 

alloys, 243 

wire, electrical table, 313, 315 
Corliss engines, 207 
Corrosion of boilers, 123 
Corrugated furnaces and flues, 162 
Coverings for steam-pipe, 42 
Current, electric, 250, 251, 260, 275 

unit of, 268 
Curvilinear seams of boilers, 100 
Cut-off", 227 

automatic, 195, 207 

valves, 207 
Cycloid gears, 24 

Daniell battery, 295 
Dead center of engines, 143 
Dead-weight safety valve, 130 
Diagrams, indicator {see Indicator) 
Draught of chimneys, 167, 171 
Ductility of metals, 238 
Dynamometers, 33, 36 
Dynamo regulation, 302 



Dynamos, 297 

compound, 302 
operated in parallel, 307 
series, 300 
shunt, 301 



Eccentric, steam engine, 199 

Eccentricity, 200 

Econouieter, 141 

Economizers, 159 

Edison 3-wire system of electrical 

distribution, 311 
Efficiency of injectors and pumps, 
relative, 152 
of pneumatic power transmis- 
sion, 28 
Ejector, 151 

Electric accumulator {see Storage 
Batteries) . 
arc lamps, 320 
batteries, 292 
bells, 341 

circuit breakers, 305 
conductivity, 270 
conductors, calculation of sizes, 
313 
insulation of, 274 
materials used {see also 
Conductors), 274 
current, heating effects, 251 
distribution of energy, 308 
parallel system, 309 
series system, 309 
3-wire system, 311 
sizes of conductors, 313 
dynamos, 297 
fuses, 305 

generators, 292, 297 
ground detectors, 305 
heating, 251 
incandescent lamps, 323 
Electric induction coil, 354 
lighting, 320 
motor generators, 332 
motors, 327 

protective devices for, 331 
pressures used in practice, 332 
resistance (see Eesistance). 
signals, 341 

storage batteries, 292, 334 
switches, 303, 305, 319 
telephones, 350 
transformer, 265 
units, 267 



361 



Electric wires, tables of weights and 
diameters, 315 

wiring, 316 
Electrical experiments, fundamen- 
tal, 248 

measurement, 285 

method of power measurement, 
34 

transmission of power, 29 
Electrolysis, 248 
Electro-magnet, 262 
Electro-motive force, 266, 267, 278 
Electro-plating, 250 
Elements, the six mechanical, 1 
Energy, conservation of, 10 

definition of, 8 

forms of, 8 

sources of, 10 
Engine, steam (see Steam engine), 175 
Exhaust, steam engine, 227 
Expansion curve, 227 

Factors of safety, 105, 245 
Fahrenheit thermometer scale, 38 
Falling bodies, motion of, 7, 8 
Feed-pumps (see Pumps). 
Feed-water, advantages of heating, 
153 
heaters, 154 

advantages of each type, 158 
closed type, 155, 156 
open type, 155, 157 
Berryman, 156 
Pittsburgh, 157 
relative advantages of pumps 
and injectors for supplying, 
152 
Field, magnetic, 254 
Firing of boilers, 163 

automatic, 165 
Fittings, boiler, 128 
Fleming's rule for direction of in- 
duced electrical currents, 260 
Flow of air, 28 
of Avater, 61 
Flues of boilers, 160 
Foaming of boilers, 123 
Force, definition of, 1 
magnetic lines of, 254 
relation between mass, accelera- 
tion, and, 10 
Forced draught, 210 

representation by lines, or 

graphically, 11 
resultant of two or more, 11 



Forces, parallelogram of, 11 

Foundations of engines, 213 

Fuels, 4 

Fulcrum, 14 

Furnaces of boilers, 160 

Fuses, 305 

Fusibility of metals, 238 

Galvanometer, 258 
Gauge cocks, 141 
Gauges, 138 

vacuum, 139 

steam pressure, 138 

water, 140 
Gearing, 23 
German silver, 243 
Governors for steam engines, 209 
Grates for boilers, 163 
Grate surface of boilers, 95, 164 
Gravity, specific, 239 
Ground detectors, 305 

Hancock inspirator, 151 
Heat, conduction of, 42 
definition of, 37 
latent, 41 

mechanical equivalent of, 42 
of combustion, 48 
radiation of, 42 
specific, 4 

transference of methods, 42 
unit of, 41 
Heaters, feed-water (see Feed-water 

Heaters). 
Heating due to electric currents, 
251 
surface of boilers, 95 
Horse-power, indicated, 229 

of boilers {.lee Centennial Rat- 
ing). 
of steam engines, calculation 
of, by indicators, 229 
rules for calculating, 177 
tables for different speeds 
and pressures, 184 
Hydrogen, 51 
in fuel, 45 
Hydrometer, 240 

Ice, weight of cubic foot, 57 
Incandescent lamps, 323 

life and efficiency of, 325 
Incrustation and scale {see Cor- 
rosion of Boilers). 



362 



Indicated horse-power (see Horse- 
power). 
Indicator cards or diagrams, 226 
function of, 225 
method of power measurement, 

of using, 226 

steam engine, 224 

Tabor, 225 
Induction coil, electric, 354 

currents of electricity, 264 
Inertia, 2 
Injectors, 146 

action of, 146 

failure of, 149 

starting, 149, 150 

setting up of, 150 

vs. pumps, 152 
Insulation of electric wires, 274 
Insulators, 274 
Intercooler, 26 
Involute gears, 24 
Iron, 240 

expansion of, due to heat, 242 

strength of, 245 

variation of strength due to 
heating, 242 

wire {see Wire). 

electrical tables, 315 

Jet condensers, 233 
Joints, riveted, 106 

Kinetic energy, 8 

Lamps, arc, 320 

incandescent, 323 
Lap of a slide valve, 200 
Latent heat, 41 
Laws of motion, Newton's, 3 
Lead, 243 

of slide valve, 200 
Leather belts, 20 
Leclanche battery, 294 
Lever, safety valve, 130 
Levers, 14 

rules for calculation, 15 
Lifters or ejectors, 151 
Lifting ejectors {see Injectors). 
Lines of force, 254 

used to represent forces ^ 11 
Link motion, 206 
Liquid fuels, 49 
Locomotive boilers, 87 



Longitudinal seams, 100 
Loss of head of water in pipes, 62 
Low-pressure cylinders {see Com- 
pound Engine). 
Lubrication, 32 

Machines, elenients of, 1 

purpose of, 1 
Magnets, electro-, 262 
Magnetic field, 254 

lines of force, 254 
Malleability of nieials, 232 
Marine boilers, 87 
Mass, definition of, 6 

relation between force, accelera- 
tion, and, 7 
relation of weight to, 6 
Materials and their properties, 236 

strength of, 244 
Mean eflTective pressure obtained 
from the indicator, 
card, 229 
of steam engines, 181, 
229 
Measurement of heights by barom- 
eter, 55 
by thermometer, 55 
Mechanical elements, 1 
equivalent of heat, 42 
firing of boilers, 165 
Mechanics, 1 
Metals, 240 

principal properties of, 238 
Methods of transmitting power, 18 
Mil, circular, 316 
Moisture in steam, 64, 65 
Molecules and molecular construc- 
tion of matter, 23 
Moment, 13 

Momentum, definition of, 7 
Motion, 3 

Newton's laws of, 3 
of falling bodies, 5 
perpetual, 4 
Motors, electric {see Electric 
Motors). 

Newton's laws of motion, 3 
Nitrogen, 45, 51, 236 
Non-condensing engine, 188 
Non-conducting covering for steam- 
pipes, 43 
Non-conductors, 274 

Ohm's law and its applications, 280 



363 



Oil separators, 32 

used as a fuel, 49 
Oils aud lubrication, 32 
Ordiuates, 230 

Over-compounded dynamos, 301 
Over-travel of a valve, 200 
Oxygen, 45, 51, 236 

Packing for steam engines, 217 
Parallel system of electrical dis- 

tributiou, 308 
Parallelogram of forces, 11 
Perpetual motion, 4 
Petroleum as a fuel, 49 
Pipe coverings, materials for, 43 
Pipes, flow of air in, 28 
of water in , 62 
Piping of engines, 216 
Piston valves, 207 
Pitch of gears, 23 
Planimeter and its use, 229 
Pneumatic transmission of power, 

25 
Ports or passages, steam, 197 
Potential energy, 8 
Power, definition of, 10 

horse-power {see also Horse- 
power), 10 
measurement, 33 
of steam engines, calculation 
of, 177 
tables of, 184 
transmission by gearing, 23 
by ropes, 22 
by shafting, 18 
electrical, 29 
methods of, 18 
pneumatic, 25 
Pressure, electric, 266, 267, 278 

mean effective, 181, 229 
Priming of boilers, 123 
Prony brake, 35 

PuUev, as a mechanical element, 
'16 
rule for calculating gain in 
force, 17 
Pumps, 142 

boiler- feed, 143 
capacity of, 145 
classification of, 142 
direct-acting, 143 
duplex, 144 
electric, 143 
fly-wheel, 143 
for hot water, 146 



Pumps, lift of, 144 

power, 142 

power required by, 145 

vs. injectoi's, 152 
Purifying feed-water, 153 

Kadiation of heat, 42 
Reaumur thermometer scale, 38 
Keceivers, compressed air, 27 

electric telephone, 352 
Reciprocating parts of steam en- 
gines, 195 
Release, 200 

Releasing valve gear, 207 
Reservoirs for compressed air, 27 
Resistance, change with change of 
temperature, 270 

electric, 251, 270 

specific, 272 
Resistances in multiple, 271 
Reversing valve-gears, 206 
Riveted joints of boilers, 106 
Rope-driving, 22 
Rubber belting, 20 
Rust, 51 

Safe current-carrying capacity of 

copper wires, 318 
Safety, factors of, 105, 245 

valves, 128 
Salinometer, 141 
Scale in boilers, 123 
Screw as a mechanical element, 1 
Seams, curvilinear, 100 

longitudinal, 100 
Separators, 171 
Series dynamos, 300 

system of electrical distribu- 
tion, 308 
Setting boilers, 109 
Shaft-governors, 211 
Shafting calculation of sizes, 19 
Shunt dynamos, 300 
Slide valves, 197 

Smoke-stack {see Stacks and Chim- 
neys). 
Specific gravity, 60, 239 

heat, 4 

resistance, 272 
Stacks for boilers, 167 

proportioning of, 168 

table of sizes for various sizes 
of boiler, 170 
Steam, 64 



364 



steam boilers {see Boilers), 
dry {see also Separators), 65 
engine, 175 

advantages of high speed, 

194 
brake, horse-power of, 177 
care and management of, 

217 
classification of, 188 
compound, 191 
condensing and non-con- 
densing, 188 
Corliss, 207 
cut-offs, 207 
foundations, 213 
governors, 209 
high- and low-speed, 194 
indicated horse-power of, 
177, 229 
tables of, at different 
piston speeds, 184 
indicator {see also Indi- 
cator), 224 
invention of, 175 
knocking in, 221 
lining up, 214 
location of, 214 
mean effective pressure of, 

181, 229 
piping for, 216 
reciprocating parts of, 195 
rotary, 196 
setting valves of, 205 
single-acting, 196 

and double-acting, 196 
and multiple expan- 
sion, 192 
throttling and automatic 

cut-off, 195 
valves and valve-gears, 197 
latent heat of, 66 
moisture in, 64 
pipe-covering, 43 
piping for engines, 216 
saturated, 45 
separators, 171 
superheated, 45 
total heat of, 67 
traps, 171 
Steel, 241 

Stoking, automatic, 166 
Storage batteries, 292, 334 
Strength of materials, 244 
String of indicator diagram, 230 
Surface condensers, 233 



Switchboards, electric, 304 
Switches, electric, 303 

Tabor indicator, 225 

Teeth, gear teeth forms, 23 

Telephone, 350 

Temperature, definition of, 38 

Tenacity of metals, 238 

Tensile strength, 244 

Theoretical indicator diagram, 227 

Thermal unit, 44 

Thermometers, 38 

Three-wire system of electric dis- 
tribution, 311 

Throttling and automatic cut-off 
engines, 195 

Throw of eccentrics, 200 

Timber, strength of, 245 

Time systems, watchmen's, 346 

Total heat, 67 

Transference of heat, 42 

Transformers, 265 

Transmitter, electric telephone, 353 

Transmission of power {see Power). 

Travel, 200 

Traps, steam, 171 

Tubular boilers {see Boilers). 

Unit of heat, 41 

of work, 8 
Units, electric, 267 

Vacuum of condensers, 234 

gauges, 139 
Valve circle, 202 

gears {see also Cut-off), 197 
releasing, 207 
reversing, 205 
the link motion, 205 
variable cut-off and revers- 
ing, 205 
Zeuner's diagram for, 202 
Valves and valve-gears, 197 
balanced, 207 
different varieties of, 207 
friction of, 206 
how to set, 205 
lap and lead of, 200 
piston, 207 
plain slide, 197 
safety, 128 
semi-rotary, 207 
separate, for admission and ex- 
haust, 207 
setting of, 205 



365 



Velocity, 4 
Volt, the, 267 

Watchmen's time systems, 34 
Water, boiling point of, 58 
columns, 140 
composition and properties, 

56 
decomposition of, 59 
flow of, 61 
specific gravity of, 59 

heat of, 58 
weight of, at diflferent tempera- 
tures, 56 
Wedge, the, 16 
Weights, atomic, 237 



Wheel and axle, the, 16 
Wire calculation of sizes for electric 
distribution, 313 
electric, tables of weights and 

diameters, 315 
properties of copper, 315 
safe-current carrying capacity 
of, 313 
Wiring, electric, 316 
Work, definition of, 8 

unit of, 8 
Wrought-iron {see Iron). 

Zero, absolute, 38 

Zeuner's diagram for valves, 202 



Ll.Ai'St? 




